Port Chromium's trace_event.h to WebKit and add

trace_event.h is ported from Chromium code.

These files are defined new for WebRTC:
* event_tracer.h
* event_tracer.cc
* event_tracer_unittest.cc
Review URL: https://webrtc-codereview.appspot.com/933034

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3262 4adac7df-926f-26a2-2b94-8c16560cd09d

6 files changed, 1250 insertions, 0 deletions

diff --git a/system_wrappers/interface/event_tracer.h b/system_wrappers/interface/event_tracer.h
new file mode 100644
index 00000000..37579254
--- /dev/null
+++ b/system_wrappers/interface/event_tracer.h
@@ -0,0 +1,77 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+// This file defines the interface for event tracing in WebRTC.
+//
+// Event log handlers are set through SetupEventTracer(). User of this API will
+// provide two function pointers to handle event tracing calls.
+//
+// * GetCategoryEnabledPtr
+//   Event tracing system calls this function to determine if a particular
+//   event category is enabled.
+//
+// * AddTraceEventPtr
+//   Adds a tracing event. It is the user's responsibility to log the data
+//   provided.
+//
+// Parameters for the above two functions are described in trace_event.h.
+
+#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_EVENT_TRACER_H_
+#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_EVENT_TRACER_H_
+
+#include "webrtc/common_types.h"
+
+namespace webrtc {
+
+typedef const unsigned char* (*GetCategoryEnabledPtr)(const char* name);
+typedef int (*AddTraceEventPtr)(char phase,
+                                const unsigned char* category_enabled,
+                                const char* name,
+                                unsigned long long id,
+                                int num_args,
+                                const char** arg_names,
+                                const unsigned char* arg_types,
+                                const unsigned long long* arg_values,
+                                int threshold_begin_id,
+                                long long threshold,
+                                unsigned char flags);
+
+// User of WebRTC can call this method to setup event tracing.
+//
+// This method must be called before any WebRTC methods. Functions
+// provided should be thread-safe.
+WEBRTC_DLLEXPORT void SetupEventTracer(
+    GetCategoryEnabledPtr get_category_enabled_ptr,
+    AddTraceEventPtr add_trace_event_ptr);
+
+// This class defines interface for the event tracing system to call
+// internally. Do not call these methods directly.
+class EventTracer {
+ public:
+  static const unsigned char* GetCategoryEnabled(
+      const char* name);
+
+  static int AddTraceEvent(
+      char phase,
+      const unsigned char* category_enabled,
+      const char* name,
+      unsigned long long id,
+      int num_args,
+      const char** arg_names,
+      const unsigned char* arg_types,
+      const unsigned long long* arg_values,
+      int threshold_begin_id,
+      long long threshold,
+      unsigned char flags);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_EVENT_TRACER_H_
diff --git a/system_wrappers/interface/trace_event.h b/system_wrappers/interface/trace_event.h
new file mode 100644
index 00000000..a7995c5c
--- /dev/null
+++ b/system_wrappers/interface/trace_event.h
@@ -0,0 +1,1018 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file under third_party_mods/chromium or at:
+// http://src.chromium.org/svn/trunk/src/LICENSE
+
+#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_TRACE_EVENT_H_
+#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_TRACE_EVENT_H_
+
+#include <string>
+
+#include "webrtc/system_wrappers/interface/atomicops.h"
+#include "webrtc/system_wrappers/interface/event_tracer.h"
+
+#if defined(TRACE_EVENT0)
+#error "Another copy of trace_event.h has already been included."
+#endif
+
+// Extracted from Chromium's src/base/debug/trace_event.h.
+
+// This header is designed to give you trace_event macros without specifying
+// how the events actually get collected and stored. If you need to expose trace
+// event to some other universe, you can copy-and-paste this file,
+// implement the TRACE_EVENT_API macros, and do any other necessary fixup for
+// the target platform. The end result is that multiple libraries can funnel
+// events through to a shared trace event collector.
+
+// Trace events are for tracking application performance and resource usage.
+// Macros are provided to track:
+//    Begin and end of function calls
+//    Counters
+//
+// Events are issued against categories. Whereas LOG's
+// categories are statically defined, TRACE categories are created
+// implicitly with a string. For example:
+//   TRACE_EVENT_INSTANT0("MY_SUBSYSTEM", "SomeImportantEvent")
+//
+// Events can be INSTANT, or can be pairs of BEGIN and END in the same scope:
+//   TRACE_EVENT_BEGIN0("MY_SUBSYSTEM", "SomethingCostly")
+//   doSomethingCostly()
+//   TRACE_EVENT_END0("MY_SUBSYSTEM", "SomethingCostly")
+// Note: our tools can't always determine the correct BEGIN/END pairs unless
+// these are used in the same scope. Use ASYNC_BEGIN/ASYNC_END macros if you
+// need them to be in separate scopes.
+//
+// A common use case is to trace entire function scopes. This
+// issues a trace BEGIN and END automatically:
+//   void doSomethingCostly() {
+//     TRACE_EVENT0("MY_SUBSYSTEM", "doSomethingCostly");
+//     ...
+//   }
+//
+// Additional parameters can be associated with an event:
+//   void doSomethingCostly2(int howMuch) {
+//     TRACE_EVENT1("MY_SUBSYSTEM", "doSomethingCostly",
+//         "howMuch", howMuch);
+//     ...
+//   }
+//
+// The trace system will automatically add to this information the
+// current process id, thread id, and a timestamp in microseconds.
+//
+// To trace an asynchronous procedure such as an IPC send/receive, use
+// ASYNC_BEGIN and ASYNC_END:
+//   [single threaded sender code]
+//     static int send_count = 0;
+//     ++send_count;
+//     TRACE_EVENT_ASYNC_BEGIN0("ipc", "message", send_count);
+//     Send(new MyMessage(send_count));
+//   [receive code]
+//     void OnMyMessage(send_count) {
+//       TRACE_EVENT_ASYNC_END0("ipc", "message", send_count);
+//     }
+// The third parameter is a unique ID to match ASYNC_BEGIN/ASYNC_END pairs.
+// ASYNC_BEGIN and ASYNC_END can occur on any thread of any traced process.
+// Pointers can be used for the ID parameter, and they will be mangled
+// internally so that the same pointer on two different processes will not
+// match. For example:
+//   class MyTracedClass {
+//    public:
+//     MyTracedClass() {
+//       TRACE_EVENT_ASYNC_BEGIN0("category", "MyTracedClass", this);
+//     }
+//     ~MyTracedClass() {
+//       TRACE_EVENT_ASYNC_END0("category", "MyTracedClass", this);
+//     }
+//   }
+//
+// Trace event also supports counters, which is a way to track a quantity
+// as it varies over time. Counters are created with the following macro:
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter", g_myCounterValue);
+//
+// Counters are process-specific. The macro itself can be issued from any
+// thread, however.
+//
+// Sometimes, you want to track two counters at once. You can do this with two
+// counter macros:
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter0", g_myCounterValue[0]);
+//   TRACE_COUNTER1("MY_SUBSYSTEM", "myCounter1", g_myCounterValue[1]);
+// Or you can do it with a combined macro:
+//   TRACE_COUNTER2("MY_SUBSYSTEM", "myCounter",
+//       "bytesPinned", g_myCounterValue[0],
+//       "bytesAllocated", g_myCounterValue[1]);
+// This indicates to the tracing UI that these counters should be displayed
+// in a single graph, as a summed area chart.
+//
+// Since counters are in a global namespace, you may want to disembiguate with a
+// unique ID, by using the TRACE_COUNTER_ID* variations.
+//
+// By default, trace collection is compiled in, but turned off at runtime.
+// Collecting trace data is the responsibility of the embedding
+// application. In Chrome's case, navigating to about:tracing will turn on
+// tracing and display data collected across all active processes.
+//
+//
+// Memory scoping note:
+// Tracing copies the pointers, not the string content, of the strings passed
+// in for category, name, and arg_names.  Thus, the following code will
+// cause problems:
+//     char* str = strdup("impprtantName");
+//     TRACE_EVENT_INSTANT0("SUBSYSTEM", str);  // BAD!
+//     free(str);                   // Trace system now has dangling pointer
+//
+// To avoid this issue with the |name| and |arg_name| parameters, use the
+// TRACE_EVENT_COPY_XXX overloads of the macros at additional runtime overhead.
+// Notes: The category must always be in a long-lived char* (i.e. static const).
+//        The |arg_values|, when used, are always deep copied with the _COPY
+//        macros.
+//
+// When are string argument values copied:
+// const char* arg_values are only referenced by default:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", "literal string is only referenced");
+// Use TRACE_STR_COPY to force copying of a const char*:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", TRACE_STR_COPY("string will be copied"));
+// std::string arg_values are always copied:
+//     TRACE_EVENT1("category", "name",
+//                  "arg1", std::string("string will be copied"));
+//
+//
+// Thread Safety:
+// Thread safety is provided by methods defined in event_tracer.h. See the file
+// for details.
+
+
+// By default, const char* argument values are assumed to have long-lived scope
+// and will not be copied. Use this macro to force a const char* to be copied.
+#define TRACE_STR_COPY(str) \
+    trace_event_internal::TraceStringWithCopy(str)
+
+// By default, uint64 ID argument values are not mangled with the Process ID in
+// TRACE_EVENT_ASYNC macros. Use this macro to force Process ID mangling.
+#define TRACE_ID_MANGLE(id) \
+    trace_event_internal::TraceID::ForceMangle(id)
+
+// Records a pair of begin and end events called "name" for the current
+// scope, with 0, 1 or 2 associated arguments. If the category is not
+// enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name)
+#define TRACE_EVENT1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, arg1_name, arg1_val)
+#define TRACE_EVENT2(category, name, arg1_name, arg1_val, arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+
+// Same as TRACE_EVENT except that they are not included in official builds.
+#ifdef OFFICIAL_BUILD
+#define UNSHIPPED_TRACE_EVENT0(category, name) (void)0
+#define UNSHIPPED_TRACE_EVENT1(category, name, arg1_name, arg1_val) (void)0
+#define UNSHIPPED_TRACE_EVENT2(category, name, arg1_name, arg1_val, \
+                               arg2_name, arg2_val) (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT0(category, name) (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val) \
+    (void)0
+#define UNSHIPPED_TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
+                                       arg2_name, arg2_val) (void)0
+#else
+#define UNSHIPPED_TRACE_EVENT0(category, name) \
+    TRACE_EVENT0(category, name)
+#define UNSHIPPED_TRACE_EVENT1(category, name, arg1_name, arg1_val) \
+    TRACE_EVENT1(category, name, arg1_name, arg1_val)
+#define UNSHIPPED_TRACE_EVENT2(category, name, arg1_name, arg1_val, \
+                               arg2_name, arg2_val) \
+    TRACE_EVENT2(category, name, arg1_name, arg1_val, arg2_name, arg2_val)
+#define UNSHIPPED_TRACE_EVENT_INSTANT0(category, name) \
+    TRACE_EVENT_INSTANT0(category, name)
+#define UNSHIPPED_TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val) \
+    TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val)
+#define UNSHIPPED_TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
+                                       arg2_name, arg2_val) \
+    TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
+                         arg2_name, arg2_val)
+#endif
+
+// Records a single event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_INSTANT0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
+        category, name, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_INSTANT1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
+        category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_INSTANT2(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
+        category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_INSTANT0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
+        category, name, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_INSTANT1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
+        category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_INSTANT2(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_INSTANT, \
+        category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+
+// Records a single BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_BEGIN0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
+        category, name, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_BEGIN1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
+        category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_BEGIN2(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
+        category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_BEGIN0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
+        category, name, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_BEGIN1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
+        category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_BEGIN2(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_BEGIN, \
+        category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+
+// Records a single END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_END0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
+        category, name, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_END1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
+        category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_END2(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
+        category, name, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_END0(category, name) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
+        category, name, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_END1(category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
+        category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_END2(category, name, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_END, \
+        category, name, TRACE_EVENT_FLAG_COPY, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+
+// Time threshold event:
+// Only record the event if the duration is greater than the specified
+// threshold_us (time in microseconds).
+// Records a pair of begin and end events called "name" for the current
+// scope, with 0, 1 or 2 associated arguments. If the category is not
+// enabled, then this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_IF_LONGER_THAN0(threshold_us, category, name) \
+    INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN(threshold_us, category, name)
+#define TRACE_EVENT_IF_LONGER_THAN1( \
+    threshold_us, category, name, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN( \
+        threshold_us, category, name, arg1_name, arg1_val)
+#define TRACE_EVENT_IF_LONGER_THAN2( \
+    threshold_us, category, name, arg1_name, arg1_val, arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN( \
+        threshold_us, category, name, arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records the value of a counter called "name" immediately. Value
+// must be representable as a 32 bit integer.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_COUNTER1(category, name, value) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, TRACE_EVENT_FLAG_NONE, \
+        "value", static_cast<int>(value))
+#define TRACE_COPY_COUNTER1(category, name, value) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, TRACE_EVENT_FLAG_COPY, \
+        "value", static_cast<int>(value))
+
+// Records the values of a multi-parted counter called "name" immediately.
+// The UI will treat value1 and value2 as parts of a whole, displaying their
+// values as a stacked-bar chart.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_COUNTER2(category, name, value1_name, value1_val, \
+        value2_name, value2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, TRACE_EVENT_FLAG_NONE, \
+        value1_name, static_cast<int>(value1_val), \
+        value2_name, static_cast<int>(value2_val))
+#define TRACE_COPY_COUNTER2(category, name, value1_name, value1_val, \
+        value2_name, value2_val) \
+    INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, TRACE_EVENT_FLAG_COPY, \
+        value1_name, static_cast<int>(value1_val), \
+        value2_name, static_cast<int>(value2_val))
+
+// Records the value of a counter called "name" immediately. Value
+// must be representable as a 32 bit integer.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to disambiguate counters with the same name. It must either
+//   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on
+//   two different processes will not collide.
+#define TRACE_COUNTER_ID1(category, name, id, value) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, \
+        "value", static_cast<int>(value))
+#define TRACE_COPY_COUNTER_ID1(category, name, id, value) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        "value", static_cast<int>(value))
+
+// Records the values of a multi-parted counter called "name" immediately.
+// The UI will treat value1 and value2 as parts of a whole, displaying their
+// values as a stacked-bar chart.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to disambiguate counters with the same name. It must either
+//   be a pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on
+//   two different processes will not collide.
+#define TRACE_COUNTER_ID2(category, name, id, value1_name, value1_val, \
+        value2_name, value2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, \
+        value1_name, static_cast<int>(value1_val), \
+        value2_name, static_cast<int>(value2_val))
+#define TRACE_COPY_COUNTER_ID2(category, name, id, value1_name, value1_val, \
+        value2_name, value2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_COUNTER, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        value1_name, static_cast<int>(value1_val), \
+        value2_name, static_cast<int>(value2_val))
+
+
+// Records a single ASYNC_BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the ASYNC_BEGIN event with the ASYNC_END event. ASYNC
+//   events are considered to match if their category, name and id values all
+//   match. |id| must either be a pointer or an integer value up to 64 bits. If
+//   it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+// An asynchronous operation can consist of multiple phases. The first phase is
+// defined by the ASYNC_BEGIN calls. Additional phases can be defined using the
+// ASYNC_STEP macros. When the operation completes, call ASYNC_END.
+// An ASYNC trace typically occur on a single thread (if not, they will only be
+// drawn on the thread defined in the ASYNC_BEGIN event), but all events in that
+// operation must use the same |name| and |id|. Each event can have its own
+// args.
+#define TRACE_EVENT_ASYNC_BEGIN0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_BEGIN1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_BEGIN2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_BEGIN2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single ASYNC_STEP event for |step| immediately. If the category
+// is not enabled, then this does nothing. The |name| and |id| must match the
+// ASYNC_BEGIN event above. The |step| param identifies this step within the
+// async event. This should be called at the beginning of the next phase of an
+// asynchronous operation.
+#define TRACE_EVENT_ASYNC_STEP0(category, name, id, step) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_ASYNC_STEP1(category, name, id, step, \
+                                      arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, "step", step, \
+        arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_STEP0(category, name, id, step) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, "step", step)
+#define TRACE_EVENT_COPY_ASYNC_STEP1(category, name, id, step, \
+        arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, "step", step, \
+        arg1_name, arg1_val)
+
+// Records a single ASYNC_END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+#define TRACE_EVENT_ASYNC_END0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+        category, name, id, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_ASYNC_END1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_ASYNC_END2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_ASYNC_END0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+        category, name, id, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_ASYNC_END1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_ASYNC_END2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_ASYNC_END, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+
+
+// Records a single FLOW_BEGIN event called "name" immediately, with 0, 1 or 2
+// associated arguments. If the category is not enabled, then this
+// does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the FLOW_BEGIN event with the FLOW_END event. FLOW
+//   events are considered to match if their category, name and id values all
+//   match. |id| must either be a pointer or an integer value up to 64 bits. If
+//   it's a pointer, the bits will be xored with a hash of the process ID so
+//   that the same pointer on two different processes will not collide.
+// FLOW events are different from ASYNC events in how they are drawn by the
+// tracing UI. A FLOW defines asynchronous data flow, such as posting a task
+// (FLOW_BEGIN) and later executing that task (FLOW_END). Expect FLOWs to be
+// drawn as lines or arrows from FLOW_BEGIN scopes to FLOW_END scopes. Similar
+// to ASYNC, a FLOW can consist of multiple phases. The first phase is defined
+// by the FLOW_BEGIN calls. Additional phases can be defined using the FLOW_STEP
+// macros. When the operation completes, call FLOW_END. An async operation can
+// span threads and processes, but all events in that operation must use the
+// same |name| and |id|. Each event can have its own args.
+#define TRACE_EVENT_FLOW_BEGIN0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_FLOW_BEGIN1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_FLOW_BEGIN2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_FLOW_BEGIN0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_FLOW_BEGIN1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_BEGIN2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_BEGIN, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+
+// Records a single FLOW_STEP event for |step| immediately. If the category
+// is not enabled, then this does nothing. The |name| and |id| must match the
+// FLOW_BEGIN event above. The |step| param identifies this step within the
+// async event. This should be called at the beginning of the next phase of an
+// asynchronous operation.
+#define TRACE_EVENT_FLOW_STEP0(category, name, id, step) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, "step", step)
+#define TRACE_EVENT_FLOW_STEP1(category, name, id, step, \
+        arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, "step", step, \
+        arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_STEP0(category, name, id, step) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, "step", step)
+#define TRACE_EVENT_COPY_FLOW_STEP1(category, name, id, step, \
+        arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_STEP, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, "step", step, \
+        arg1_name, arg1_val)
+
+// Records a single FLOW_END event for "name" immediately. If the category
+// is not enabled, then this does nothing.
+#define TRACE_EVENT_FLOW_END0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, \
+        category, name, id, TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_FLOW_END1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val)
+#define TRACE_EVENT_FLOW_END2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, \
+        category, name, id, TRACE_EVENT_FLAG_NONE, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+#define TRACE_EVENT_COPY_FLOW_END0(category, name, id) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, \
+        category, name, id, TRACE_EVENT_FLAG_COPY)
+#define TRACE_EVENT_COPY_FLOW_END1(category, name, id, arg1_name, arg1_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val)
+#define TRACE_EVENT_COPY_FLOW_END2(category, name, id, arg1_name, arg1_val, \
+        arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_FLOW_END, \
+        category, name, id, TRACE_EVENT_FLAG_COPY, \
+        arg1_name, arg1_val, arg2_name, arg2_val)
+
+
+////////////////////////////////////////////////////////////////////////////////
+// Implementation specific tracing API definitions.
+
+// Get a pointer to the enabled state of the given trace category. Only
+// long-lived literal strings should be given as the category name. The returned
+// pointer can be held permanently in a local static for example. If the
+// unsigned char is non-zero, tracing is enabled. If tracing is enabled,
+// TRACE_EVENT_API_ADD_TRACE_EVENT can be called. It's OK if tracing is disabled
+// between the load of the tracing state and the call to
+// TRACE_EVENT_API_ADD_TRACE_EVENT, because this flag only provides an early out
+// for best performance when tracing is disabled.
+// const unsigned char*
+//     TRACE_EVENT_API_GET_CATEGORY_ENABLED(const char* category_name)
+#define TRACE_EVENT_API_GET_CATEGORY_ENABLED \
+    webrtc::EventTracer::GetCategoryEnabled
+
+// Add a trace event to the platform tracing system. Returns thresholdBeginId
+// for use in a corresponding end TRACE_EVENT_API_ADD_TRACE_EVENT call.
+// int TRACE_EVENT_API_ADD_TRACE_EVENT(
+//                    char phase,
+//                    const unsigned char* category_enabled,
+//                    const char* name,
+//                    unsigned long long id,
+//                    int num_args,
+//                    const char** arg_names,
+//                    const unsigned char* arg_types,
+//                    const unsigned long long* arg_values,
+//                    int threshold_begin_id,
+//                    long long threshold,
+//                    unsigned char flags)
+#define TRACE_EVENT_API_ADD_TRACE_EVENT webrtc::EventTracer::AddTraceEvent
+
+////////////////////////////////////////////////////////////////////////////////
+
+// Implementation detail: trace event macros create temporary variables
+// to keep instrumentation overhead low. These macros give each temporary
+// variable a unique name based on the line number to prevent name collissions.
+#define INTERNAL_TRACE_EVENT_UID3(a,b) \
+    trace_event_unique_##a##b
+#define INTERNAL_TRACE_EVENT_UID2(a,b) \
+    INTERNAL_TRACE_EVENT_UID3(a,b)
+#define INTERNAL_TRACE_EVENT_UID(name_prefix) \
+    INTERNAL_TRACE_EVENT_UID2(name_prefix, __LINE__)
+
+// Implementation detail: internal macro to create static category.
+// No barriers are needed, because this code is designed to operate safely
+// even when the unsigned char* points to garbage data (which may be the case
+// on processors without cache coherency).
+#define INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category) \
+    static webrtc::subtle::AtomicWord INTERNAL_TRACE_EVENT_UID(atomic) = 0; \
+    const uint8_t* INTERNAL_TRACE_EVENT_UID(catstatic) = \
+        reinterpret_cast<const uint8_t*>( \
+            webrtc::subtle::NoBarrier_Load( \
+                &INTERNAL_TRACE_EVENT_UID(atomic))); \
+    if (!INTERNAL_TRACE_EVENT_UID(catstatic)) { \
+      INTERNAL_TRACE_EVENT_UID(catstatic) = \
+          TRACE_EVENT_API_GET_CATEGORY_ENABLED(category); \
+      webrtc::subtle::NoBarrier_Store(&INTERNAL_TRACE_EVENT_UID(atomic), \
+          reinterpret_cast<webrtc::subtle::AtomicWord>( \
+              INTERNAL_TRACE_EVENT_UID(catstatic))); \
+    }
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD(phase, category, name, flags, ...) \
+    do { \
+      INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
+      if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
+        trace_event_internal::AddTraceEvent( \
+            phase, INTERNAL_TRACE_EVENT_UID(catstatic), name, \
+            trace_event_internal::kNoEventId, flags, ##__VA_ARGS__); \
+      } \
+    } while (0)
+
+// Implementation detail: internal macro to create static category and add begin
+// event if the category is enabled. Also adds the end event when the scope
+// ends.
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED(category, name, ...) \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
+    trace_event_internal::TraceEndOnScopeClose \
+        INTERNAL_TRACE_EVENT_UID(profileScope); \
+    if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
+      trace_event_internal::AddTraceEvent( \
+          TRACE_EVENT_PHASE_BEGIN, \
+          INTERNAL_TRACE_EVENT_UID(catstatic), \
+          name, trace_event_internal::kNoEventId, \
+          TRACE_EVENT_FLAG_NONE, ##__VA_ARGS__); \
+      INTERNAL_TRACE_EVENT_UID(profileScope).Initialize( \
+          INTERNAL_TRACE_EVENT_UID(catstatic), name); \
+    }
+
+// Implementation detail: internal macro to create static category and add begin
+// event if the category is enabled. Also adds the end event when the scope
+// ends. If the elapsed time is < threshold time, the begin/end pair is erased.
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED_IF_LONGER_THAN(threshold, \
+        category, name, ...) \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
+    trace_event_internal::TraceEndOnScopeCloseThreshold \
+        INTERNAL_TRACE_EVENT_UID(profileScope); \
+    if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
+      int INTERNAL_TRACE_EVENT_UID(begin_event_id) = \
+        trace_event_internal::AddTraceEvent( \
+            TRACE_EVENT_PHASE_BEGIN, \
+            INTERNAL_TRACE_EVENT_UID(catstatic), \
+            name, trace_event_internal::kNoEventId, \
+            TRACE_EVENT_FLAG_NONE, ##__VA_ARGS__); \
+      INTERNAL_TRACE_EVENT_UID(profileScope).Initialize( \
+          INTERNAL_TRACE_EVENT_UID(catstatic), name, \
+          INTERNAL_TRACE_EVENT_UID(begin_event_id), threshold); \
+    }
+
+// Implementation detail: internal macro to create static category and add
+// event if the category is enabled.
+#define INTERNAL_TRACE_EVENT_ADD_WITH_ID(phase, category, name, id, flags, \
+                                         ...) \
+    do { \
+      INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
+      if (*INTERNAL_TRACE_EVENT_UID(catstatic)) { \
+        unsigned char trace_event_flags = flags | TRACE_EVENT_FLAG_HAS_ID; \
+        trace_event_internal::TraceID trace_event_trace_id( \
+            id, &trace_event_flags); \
+        trace_event_internal::AddTraceEvent( \
+            phase, INTERNAL_TRACE_EVENT_UID(catstatic), \
+            name, trace_event_trace_id.data(), trace_event_flags, \
+            ##__VA_ARGS__); \
+      } \
+    } while (0)
+
+// Notes regarding the following definitions:
+// New values can be added and propagated to third party libraries, but existing
+// definitions must never be changed, because third party libraries may use old
+// definitions.
+
+// Phase indicates the nature of an event entry. E.g. part of a begin/end pair.
+#define TRACE_EVENT_PHASE_BEGIN    ('B')
+#define TRACE_EVENT_PHASE_END      ('E')
+#define TRACE_EVENT_PHASE_INSTANT  ('I')
+#define TRACE_EVENT_PHASE_ASYNC_BEGIN ('S')
+#define TRACE_EVENT_PHASE_ASYNC_STEP  ('T')
+#define TRACE_EVENT_PHASE_ASYNC_END   ('F')
+#define TRACE_EVENT_PHASE_FLOW_BEGIN ('s')
+#define TRACE_EVENT_PHASE_FLOW_STEP  ('t')
+#define TRACE_EVENT_PHASE_FLOW_END   ('f')
+#define TRACE_EVENT_PHASE_METADATA ('M')
+#define TRACE_EVENT_PHASE_COUNTER  ('C')
+
+// Flags for changing the behavior of TRACE_EVENT_API_ADD_TRACE_EVENT.
+#define TRACE_EVENT_FLAG_NONE        (static_cast<unsigned char>(0))
+#define TRACE_EVENT_FLAG_COPY        (static_cast<unsigned char>(1 << 0))
+#define TRACE_EVENT_FLAG_HAS_ID      (static_cast<unsigned char>(1 << 1))
+#define TRACE_EVENT_FLAG_MANGLE_ID   (static_cast<unsigned char>(1 << 2))
+
+// Type values for identifying types in the TraceValue union.
+#define TRACE_VALUE_TYPE_BOOL         (static_cast<unsigned char>(1))
+#define TRACE_VALUE_TYPE_UINT         (static_cast<unsigned char>(2))
+#define TRACE_VALUE_TYPE_INT          (static_cast<unsigned char>(3))
+#define TRACE_VALUE_TYPE_DOUBLE       (static_cast<unsigned char>(4))
+#define TRACE_VALUE_TYPE_POINTER      (static_cast<unsigned char>(5))
+#define TRACE_VALUE_TYPE_STRING       (static_cast<unsigned char>(6))
+#define TRACE_VALUE_TYPE_COPY_STRING  (static_cast<unsigned char>(7))
+
+namespace trace_event_internal {
+
+// Specify these values when the corresponding argument of AddTraceEvent is not
+// used.
+const int kZeroNumArgs = 0;
+const int kNoThreshholdBeginId = -1;
+const long long kNoThresholdValue = 0;
+const unsigned long long kNoEventId = 0;
+
+// TraceID encapsulates an ID that can either be an integer or pointer. Pointers
+// are mangled with the Process ID so that they are unlikely to collide when the
+// same pointer is used on different processes.
+class TraceID {
+ public:
+  class ForceMangle {
+    public:
+     explicit ForceMangle(unsigned long long id) : data_(id) {}
+     explicit ForceMangle(unsigned long id) : data_(id) {}
+     explicit ForceMangle(unsigned int id) : data_(id) {}
+     explicit ForceMangle(unsigned short id) : data_(id) {}
+     explicit ForceMangle(unsigned char id) : data_(id) {}
+     explicit ForceMangle(long long id)
+         : data_(static_cast<unsigned long long>(id)) {}
+     explicit ForceMangle(long id)
+         : data_(static_cast<unsigned long long>(id)) {}
+     explicit ForceMangle(int id)
+         : data_(static_cast<unsigned long long>(id)) {}
+     explicit ForceMangle(short id)
+         : data_(static_cast<unsigned long long>(id)) {}
+     explicit ForceMangle(signed char id)
+         : data_(static_cast<unsigned long long>(id)) {}
+
+     unsigned long long data() const { return data_; }
+
+    private:
+     unsigned long long data_;
+  };
+
+  explicit TraceID(const void* id, unsigned char* flags)
+      : data_(static_cast<unsigned long long>(
+              reinterpret_cast<unsigned long>(id))) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  explicit TraceID(ForceMangle id, unsigned char* flags) : data_(id.data()) {
+    *flags |= TRACE_EVENT_FLAG_MANGLE_ID;
+  }
+  explicit TraceID(unsigned long long id, unsigned char* flags)
+      : data_(id) { (void)flags; }
+  explicit TraceID(unsigned long id, unsigned char* flags)
+      : data_(id) { (void)flags; }
+  explicit TraceID(unsigned int id, unsigned char* flags)
+      : data_(id) { (void)flags; }
+  explicit TraceID(unsigned short id, unsigned char* flags)
+      : data_(id) { (void)flags; }
+  explicit TraceID(unsigned char id, unsigned char* flags)
+      : data_(id) { (void)flags; }
+  explicit TraceID(long long id, unsigned char* flags)
+      : data_(static_cast<unsigned long long>(id)) { (void)flags; }
+  explicit TraceID(long id, unsigned char* flags)
+      : data_(static_cast<unsigned long long>(id)) { (void)flags; }
+  explicit TraceID(int id, unsigned char* flags)
+      : data_(static_cast<unsigned long long>(id)) { (void)flags; }
+  explicit TraceID(short id, unsigned char* flags)
+      : data_(static_cast<unsigned long long>(id)) { (void)flags; }
+  explicit TraceID(signed char id, unsigned char* flags)
+      : data_(static_cast<unsigned long long>(id)) { (void)flags; }
+
+  unsigned long long data() const { return data_; }
+
+ private:
+  unsigned long long data_;
+};
+
+// Simple union to store various types as unsigned long long.
+union TraceValueUnion {
+  bool as_bool;
+  unsigned long long as_uint;
+  long long as_int;
+  double as_double;
+  const void* as_pointer;
+  const char* as_string;
+};
+
+// Simple container for const char* that should be copied instead of retained.
+class TraceStringWithCopy {
+ public:
+  explicit TraceStringWithCopy(const char* str) : str_(str) {}
+  operator const char* () const { return str_; }
+ private:
+  const char* str_;
+};
+
+// Define SetTraceValue for each allowed type. It stores the type and
+// value in the return arguments. This allows this API to avoid declaring any
+// structures so that it is portable to third_party libraries.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE(actual_type, \
+                                         union_member, \
+                                         value_type_id) \
+    static inline void SetTraceValue(actual_type arg, \
+                                     unsigned char* type, \
+                                     unsigned long long* value) { \
+      TraceValueUnion type_value; \
+      type_value.union_member = arg; \
+      *type = value_type_id; \
+      *value = type_value.as_uint; \
+    }
+// Simpler form for int types that can be safely casted.
+#define INTERNAL_DECLARE_SET_TRACE_VALUE_INT(actual_type, \
+                                             value_type_id) \
+    static inline void SetTraceValue(actual_type arg, \
+                                     unsigned char* type, \
+                                     unsigned long long* value) { \
+      *type = value_type_id; \
+      *value = static_cast<unsigned long long>(arg); \
+    }
+
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned long long, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned long, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned int, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned short, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(unsigned char, TRACE_VALUE_TYPE_UINT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(long long, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(long, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(int, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(short, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE_INT(signed char, TRACE_VALUE_TYPE_INT)
+INTERNAL_DECLARE_SET_TRACE_VALUE(bool, as_bool, TRACE_VALUE_TYPE_BOOL)
+INTERNAL_DECLARE_SET_TRACE_VALUE(double, as_double, TRACE_VALUE_TYPE_DOUBLE)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const void*, as_pointer,
+                                 TRACE_VALUE_TYPE_POINTER)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const char*, as_string,
+                                 TRACE_VALUE_TYPE_STRING)
+INTERNAL_DECLARE_SET_TRACE_VALUE(const TraceStringWithCopy&, as_string,
+                                 TRACE_VALUE_TYPE_COPY_STRING)
+
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE
+#undef INTERNAL_DECLARE_SET_TRACE_VALUE_INT
+
+// std::string version of SetTraceValue so that trace arguments can be strings.
+static inline void SetTraceValue(const std::string& arg,
+                                 unsigned char* type,
+                                 unsigned long long* value) {
+  TraceValueUnion type_value;
+  type_value.as_string = arg.c_str();
+  *type = TRACE_VALUE_TYPE_COPY_STRING;
+  *value = type_value.as_uint;
+}
+
+// These AddTraceEvent template functions are defined here instead of in the
+// macro, because the arg_values could be temporary objects, such as
+// std::string. In order to store pointers to the internal c_str and pass
+// through to the tracing API, the arg_values must live throughout
+// these procedures.
+
+static inline int AddTraceEvent(char phase,
+                                const unsigned char* category_enabled,
+                                const char* name,
+                                unsigned long long id,
+                                unsigned char flags) {
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_enabled, name, id,
+      kZeroNumArgs, NULL, NULL, NULL,
+      kNoThreshholdBeginId, kNoThresholdValue, flags);
+}
+
+template<class ARG1_TYPE>
+static inline int AddTraceEvent(char phase,
+                                const unsigned char* category_enabled,
+                                const char* name,
+                                unsigned long long id,
+                                unsigned char flags,
+                                const char* arg1_name,
+                                const ARG1_TYPE& arg1_val) {
+  const int num_args = 1;
+  unsigned char arg_types[1];
+  unsigned long long arg_values[1];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_enabled, name, id,
+      num_args, &arg1_name, arg_types, arg_values,
+      kNoThreshholdBeginId, kNoThresholdValue, flags);
+}
+
+template<class ARG1_TYPE, class ARG2_TYPE>
+static inline int AddTraceEvent(char phase,
+                                const unsigned char* category_enabled,
+                                const char* name,
+                                unsigned long long id,
+                                unsigned char flags,
+                                const char* arg1_name,
+                                const ARG1_TYPE& arg1_val,
+                                const char* arg2_name,
+                                const ARG2_TYPE& arg2_val) {
+  const int num_args = 2;
+  const char* arg_names[2] = { arg1_name, arg2_name };
+  unsigned char arg_types[2];
+  unsigned long long arg_values[2];
+  SetTraceValue(arg1_val, &arg_types[0], &arg_values[0]);
+  SetTraceValue(arg2_val, &arg_types[1], &arg_values[1]);
+  return TRACE_EVENT_API_ADD_TRACE_EVENT(
+      phase, category_enabled, name, id,
+      num_args, arg_names, arg_types, arg_values,
+      kNoThreshholdBeginId, kNoThresholdValue, flags);
+}
+
+// Used by TRACE_EVENTx macro. Do not use directly.
+class TraceEndOnScopeClose {
+ public:
+  // Note: members of data_ intentionally left uninitialized. See Initialize.
+  TraceEndOnScopeClose() : p_data_(NULL) {}
+  ~TraceEndOnScopeClose() {
+    if (p_data_)
+      AddEventIfEnabled();
+  }
+
+  void Initialize(const unsigned char* category_enabled,
+                  const char* name) {
+    data_.category_enabled = category_enabled;
+    data_.name = name;
+    p_data_ = &data_;
+  }
+
+ private:
+  // Add the end event if the category is still enabled.
+  void AddEventIfEnabled() {
+    // Only called when p_data_ is non-null.
+    if (*p_data_->category_enabled) {
+      TRACE_EVENT_API_ADD_TRACE_EVENT(
+          TRACE_EVENT_PHASE_END,
+          p_data_->category_enabled,
+          p_data_->name, kNoEventId,
+          kZeroNumArgs, NULL, NULL, NULL,
+          kNoThreshholdBeginId, kNoThresholdValue, TRACE_EVENT_FLAG_NONE);
+    }
+  }
+
+  // This Data struct workaround is to avoid initializing all the members
+  // in Data during construction of this object, since this object is always
+  // constructed, even when tracing is disabled. If the members of Data were
+  // members of this class instead, compiler warnings occur about potential
+  // uninitialized accesses.
+  struct Data {
+    const unsigned char* category_enabled;
+    const char* name;
+  };
+  Data* p_data_;
+  Data data_;
+};
+
+// Used by TRACE_EVENTx macro. Do not use directly.
+class TraceEndOnScopeCloseThreshold {
+ public:
+  // Note: members of data_ intentionally left uninitialized. See Initialize.
+  TraceEndOnScopeCloseThreshold() : p_data_(NULL) {}
+  ~TraceEndOnScopeCloseThreshold() {
+    if (p_data_)
+      AddEventIfEnabled();
+  }
+
+  // Called by macros only when tracing is enabled at the point when the begin
+  // event is added.
+  void Initialize(const unsigned char* category_enabled,
+                  const char* name,
+                  int threshold_begin_id,
+                  long long threshold) {
+    data_.category_enabled = category_enabled;
+    data_.name = name;
+    data_.threshold_begin_id = threshold_begin_id;
+    data_.threshold = threshold;
+    p_data_ = &data_;
+  }
+
+ private:
+  // Add the end event if the category is still enabled.
+  void AddEventIfEnabled() {
+    // Only called when p_data_ is non-null.
+    if (*p_data_->category_enabled) {
+      TRACE_EVENT_API_ADD_TRACE_EVENT(
+          TRACE_EVENT_PHASE_END,
+          p_data_->category_enabled,
+          p_data_->name, kNoEventId,
+          kZeroNumArgs, NULL, NULL, NULL,
+          p_data_->threshold_begin_id, p_data_->threshold,
+          TRACE_EVENT_FLAG_NONE);
+    }
+  }
+
+  // This Data struct workaround is to avoid initializing all the members
+  // in Data during construction of this object, since this object is always
+  // constructed, even when tracing is disabled. If the members of Data were
+  // members of this class instead, compiler warnings occur about potential
+  // uninitialized accesses.
+  struct Data {
+    long long threshold;
+    const unsigned char* category_enabled;
+    const char* name;
+    int threshold_begin_id;
+  };
+  Data* p_data_;
+  Data data_;
+};
+
+}  // namespace trace_event_internal
+
+#endif  // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_TRACE_EVENT_H_
diff --git a/system_wrappers/source/Android.mk b/system_wrappers/source/Android.mk
index 7c77d491..f59d8806 100644
--- a/system_wrappers/source/Android.mk
+++ b/system_wrappers/source/Android.mk
@@ -29,6 +29,7 @@ LOCAL_SRC_FILES := \
     cpu_info.cc \
     critical_section.cc \
     event.cc \
+    event_tracer.cc \
     file_impl.cc \
     list_no_stl.cc \
     rw_lock.cc \
diff --git a/system_wrappers/source/event_tracer.cc b/system_wrappers/source/event_tracer.cc
new file mode 100644
index 00000000..e7114e35
--- /dev/null
+++ b/system_wrappers/source/event_tracer.cc
@@ -0,0 +1,65 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/system_wrappers/interface/event_tracer.h"
+
+namespace webrtc {
+
+namespace {
+
+GetCategoryEnabledPtr g_get_category_enabled_ptr = 0;
+AddTraceEventPtr g_add_trace_event_ptr = 0;
+
+}  // namespace
+
+void SetupEventTracer(GetCategoryEnabledPtr get_category_enabled_ptr,
+                      AddTraceEventPtr add_trace_event_ptr) {
+  g_get_category_enabled_ptr = get_category_enabled_ptr;
+  g_add_trace_event_ptr = add_trace_event_ptr;
+}
+
+// static
+const unsigned char* EventTracer::GetCategoryEnabled(const char* name) {
+  if (g_get_category_enabled_ptr)
+    return g_get_category_enabled_ptr(name);
+
+  // A string with null terminator means category is disabled.
+  return reinterpret_cast<const unsigned char*>("\0");
+}
+
+// static
+int EventTracer::AddTraceEvent(char phase,
+                               const unsigned char* category_enabled,
+                               const char* name,
+                               unsigned long long id,
+                               int num_args,
+                               const char** arg_names,
+                               const unsigned char* arg_types,
+                               const unsigned long long* arg_values,
+                               int threshold_begin_id,
+                               long long threshold,
+                               unsigned char flags) {
+  if (g_add_trace_event_ptr) {
+    return g_add_trace_event_ptr(phase,
+                                 category_enabled,
+                                 name,
+                                 id,
+                                 num_args,
+                                 arg_names,
+                                 arg_types,
+                                 arg_values,
+                                 threshold_begin_id,
+                                 threshold,
+                                 flags);
+  }
+  return -1;
+}
+
+}  // namespace webrtc
diff --git a/system_wrappers/source/event_tracer_unittest.cc b/system_wrappers/source/event_tracer_unittest.cc
new file mode 100644
index 00000000..f6a561b0
--- /dev/null
+++ b/system_wrappers/source/event_tracer_unittest.cc
@@ -0,0 +1,85 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/system_wrappers/interface/event_tracer.h"
+
+#include "gtest/gtest.h"
+#include "webrtc/system_wrappers/interface/static_instance.h"
+#include "webrtc/system_wrappers/interface/trace_event.h"
+
+namespace {
+
+class TestStatistics {
+ public:
+  TestStatistics() : events_logged_(0) {
+  }
+
+  void Reset() {
+    events_logged_ = 0;
+  }
+
+  void Increment() {
+    ++events_logged_;
+  }
+
+  int Count() const { return events_logged_; }
+
+  static TestStatistics* Get() {
+    static TestStatistics* test_stats = NULL;
+    if (!test_stats)
+      test_stats = new TestStatistics();
+    return test_stats;
+  }
+
+ private:
+  int events_logged_;
+};
+
+static const unsigned char* GetCategoryEnabledHandler(const char* name) {
+  return reinterpret_cast<const unsigned char*>("test");
+}
+
+static int AddTraceEventHandler(char phase,
+                                const unsigned char* category_enabled,
+                                const char* name,
+                                unsigned long long id,
+                                int num_args,
+                                const char** arg_names,
+                                const unsigned char* arg_types,
+                                const unsigned long long* arg_values,
+                                int threshold_begin_id,
+                                long long threshold,
+                                unsigned char flags) {
+  TestStatistics::Get()->Increment();
+  return 1;
+}
+
+}  // namespace
+
+namespace webrtc {
+
+TEST(EventTracerTest, EventTracerDisabled) {
+  {
+    TRACE_EVENT0("test", "EventTracerDisabled");
+  }
+  EXPECT_FALSE(TestStatistics::Get()->Count());
+  TestStatistics::Get()->Reset();
+}
+
+TEST(EventTracerTest, ScopedTraceEvent) {
+  SetupEventTracer(&GetCategoryEnabledHandler, &AddTraceEventHandler);
+  {
+    TRACE_EVENT0("test", "ScopedTraceEvent");
+  }
+  EXPECT_EQ(2, TestStatistics::Get()->Count());
+  TestStatistics::Get()->Reset();
+}
+
+}  // namespace webrtc
diff --git a/system_wrappers/source/system_wrappers.gyp b/system_wrappers/source/system_wrappers.gyp
index 1d4d7643..11a76196 100644
--- a/system_wrappers/source/system_wrappers.gyp
+++ b/system_wrappers/source/system_wrappers.gyp
@@ -40,6 +40,7 @@
         '../interface/data_log.h',
         '../interface/data_log_c.h',
         '../interface/data_log_impl.h',
+        '../interface/event_tracer.h',
         '../interface/event_wrapper.h',
         '../interface/file_wrapper.h',
         '../interface/fix_interlocked_exchange_pointer_win.h',
@@ -56,6 +57,7 @@
         '../interface/thread_wrapper.h',
         '../interface/tick_util.h',
         '../interface/trace.h',
+        '../interface/trace_event.h',
         'aligned_malloc.cc',
         'atomic32_mac.cc',
         'atomic32_posix.cc',
@@ -87,6 +89,7 @@
         'event.cc',
         'event_posix.cc',
         'event_posix.h',
+        'event_tracer.cc',
         'event_win.cc',
         'event_win.h',
         'file_impl.cc',
@@ -248,6 +251,7 @@
             'cpu_measurement_harness.h',
             'cpu_measurement_harness.cc',
             'critical_section_unittest.cc',
+            'event_tracer_unittest.cc',
             'list_unittest.cc',
             'logging_unittest.cc',
             'map_unittest.cc',