Add ALLOW_UNUSED and update COMPILE_ASSERT to Chromium's latest.

Fixes building with gcc 4.8.

TBR=fdegans@google.com
BUG=chromium:321833

Review URL: https://webrtc-codereview.appspot.com/12439004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@6050 4adac7df-926f-26a2-2b94-8c16560cd09d

2 files changed, 21 insertions, 3 deletions

diff --git a/system_wrappers/interface/compile_assert.h b/system_wrappers/interface/compile_assert.h
index cdeaa567..46e40ac4 100644
--- a/system_wrappers/interface/compile_assert.h
+++ b/system_wrappers/interface/compile_assert.h
@@ -8,7 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-// Borrowed from Chromium's src/base/basictypes.h.
+// Borrowed from Chromium's src/base/macros.h.
 
 #ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_
 #define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_
@@ -31,13 +31,20 @@
 // TODO(ajm): Hack to avoid multiple definitions until the base/ of webrtc and
 // libjingle are merged.
 #if !defined(COMPILE_ASSERT)
+#if __cplusplus >= 201103L
+// Under C++11, just use static_assert.
+#define COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
+
+#else
 template <bool>
 struct CompileAssert {
 };
 
 #define COMPILE_ASSERT(expr, msg) \
-  typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1]
-#endif  // COMPILE_ASSERT
+  typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] ALLOW_UNUSED
+
+#endif  //  __cplusplus >= 201103L
+#endif  //  !defined(COMPILE_ASSERT)
 
 // Implementation details of COMPILE_ASSERT:
 //
diff --git a/typedefs.h b/typedefs.h
index d8977ff4..d9328c67 100644
--- a/typedefs.h
+++ b/typedefs.h
@@ -96,6 +96,17 @@ typedef unsigned __int64    uint64_t;
 #define OVERRIDE
 #endif
 
+// Annotate a variable indicating it's ok if the variable is not used.
+// (Typically used to silence a compiler warning when the assignment
+// is important for some other reason.)
+// Use like:
+//   int x ALLOW_UNUSED = ...;
+#if defined(__GNUC__)
+#define ALLOW_UNUSED __attribute__((unused))
+#else
+#define ALLOW_UNUSED
+#endif
+
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() WARN_UNUSED_RESULT;