libchrome: Uprev the library to r456626 from Chromium

Pulled the latest and greatest version of libchrome from Chromium.

The merge was done against r456626 which corresponds to git commit
08266b3fca707804065a2cfd60331722ade41969 of Mar 14, 2017

Notable changes are:
- FOR_EACH_OBSERVER macro removed (replaced by use of C++ 11
  range-base for loop)
  - base::Values no more FundamentalValue
  - stl_util moved to base namespace
  - some scoped pointers removed in crypto/ in favor
    of BoringSSL UniquePtr.
    - path() accessor renamed to GetPath() in ScopedTempDir (and other
      classes)
      - introduction of base::CallbackOnce

Test: All unit-tests should still pass.
Change-Id: I1e65efb167fa708e35ed7c6492f1cb66a6a46104
Merged-In: I180f9defc7607f462389fae17701fff553c4a2d0

1 files changed, 106 insertions, 358 deletions

diff --git a/base/callback.h b/base/callback.h
index e087c731d1..40bd5208a8 100644
--- a/base/callback.h
+++ b/base/callback.h
@@ -12,382 +12,130 @@
 // Closure should #include "base/callback_forward.h" instead of this file.
 
 // -----------------------------------------------------------------------------
-// Introduction
+// Usage documentation
 // -----------------------------------------------------------------------------
 //
-// The templated Callback class is a generalized function object. Together
-// with the Bind() function in bind.h, they provide a type-safe method for
-// performing partial application of functions.
-//
-// Partial application (or "currying") is the process of binding a subset of
-// a function's arguments to produce another function that takes fewer
-// arguments. This can be used to pass around a unit of delayed execution,
-// much like lexical closures are used in other languages. For example, it
-// is used in Chromium code to schedule tasks on different MessageLoops.
-//
-// A callback with no unbound input parameters (base::Callback<void()>)
-// is called a base::Closure. Note that this is NOT the same as what other
-// languages refer to as a closure -- it does not retain a reference to its
-// enclosing environment.
-//
-// MEMORY MANAGEMENT AND PASSING
-//
-// The Callback objects themselves should be passed by const-reference, and
-// stored by copy. They internally store their state via a refcounted class
-// and thus do not need to be deleted.
-//
-// The reason to pass via a const-reference is to avoid unnecessary
-// AddRef/Release pairs to the internal state.
-//
-//
-// -----------------------------------------------------------------------------
-// Quick reference for basic stuff
-// -----------------------------------------------------------------------------
-//
-// BINDING A BARE FUNCTION
-//
-//   int Return5() { return 5; }
-//   base::Callback<int()> func_cb = base::Bind(&Return5);
-//   LOG(INFO) << func_cb.Run();  // Prints 5.
-//
-// BINDING A CLASS METHOD
-//
-//   The first argument to bind is the member function to call, the second is
-//   the object on which to call it.
-//
-//   class Ref : public base::RefCountedThreadSafe<Ref> {
-//    public:
-//     int Foo() { return 3; }
-//     void PrintBye() { LOG(INFO) << "bye."; }
-//   };
-//   scoped_refptr<Ref> ref = new Ref();
-//   base::Callback<void()> ref_cb = base::Bind(&Ref::Foo, ref);
-//   LOG(INFO) << ref_cb.Run();  // Prints out 3.
-//
-//   By default the object must support RefCounted or you will get a compiler
-//   error. If you're passing between threads, be sure it's
-//   RefCountedThreadSafe! See "Advanced binding of member functions" below if
-//   you don't want to use reference counting.
-//
-// RUNNING A CALLBACK
-//
-//   Callbacks can be run with their "Run" method, which has the same
-//   signature as the template argument to the callback.
-//
-//   void DoSomething(const base::Callback<void(int, std::string)>& callback) {
-//     callback.Run(5, "hello");
-//   }
-//
-//   Callbacks can be run more than once (they don't get deleted or marked when
-//   run). However, this precludes using base::Passed (see below).
-//
-//   void DoSomething(const base::Callback<double(double)>& callback) {
-//     double myresult = callback.Run(3.14159);
-//     myresult += callback.Run(2.71828);
-//   }
-//
-// PASSING UNBOUND INPUT PARAMETERS
-//
-//   Unbound parameters are specified at the time a callback is Run(). They are
-//   specified in the Callback template type:
-//
-//   void MyFunc(int i, const std::string& str) {}
-//   base::Callback<void(int, const std::string&)> cb = base::Bind(&MyFunc);
-//   cb.Run(23, "hello, world");
-//
-// PASSING BOUND INPUT PARAMETERS
-//
-//   Bound parameters are specified when you create thee callback as arguments
-//   to Bind(). They will be passed to the function and the Run()ner of the
-//   callback doesn't see those values or even know that the function it's
-//   calling.
-//
-//   void MyFunc(int i, const std::string& str) {}
-//   base::Callback<void()> cb = base::Bind(&MyFunc, 23, "hello world");
-//   cb.Run();
-//
-//   A callback with no unbound input parameters (base::Callback<void()>)
-//   is called a base::Closure. So we could have also written:
-//
-//   base::Closure cb = base::Bind(&MyFunc, 23, "hello world");
-//
-//   When calling member functions, bound parameters just go after the object
-//   pointer.
-//
-//   base::Closure cb = base::Bind(&MyClass::MyFunc, this, 23, "hello world");
-//
-// PARTIAL BINDING OF PARAMETERS
-//
-//   You can specify some parameters when you create the callback, and specify
-//   the rest when you execute the callback.
-//
-//   void MyFunc(int i, const std::string& str) {}
-//   base::Callback<void(const std::string&)> cb = base::Bind(&MyFunc, 23);
-//   cb.Run("hello world");
-//
-//   When calling a function bound parameters are first, followed by unbound
-//   parameters.
-//
-//
-// -----------------------------------------------------------------------------
-// Quick reference for advanced binding
-// -----------------------------------------------------------------------------
-//
-// BINDING A CLASS METHOD WITH WEAK POINTERS
-//
-//   base::Bind(&MyClass::Foo, GetWeakPtr());
-//
-//   The callback will not be run if the object has already been destroyed.
-//   DANGER: weak pointers are not threadsafe, so don't use this
-//   when passing between threads!
-//
-// BINDING A CLASS METHOD WITH MANUAL LIFETIME MANAGEMENT
-//
-//   base::Bind(&MyClass::Foo, base::Unretained(this));
-//
-//   This disables all lifetime management on the object. You're responsible
-//   for making sure the object is alive at the time of the call. You break it,
-//   you own it!
-//
-// BINDING A CLASS METHOD AND HAVING THE CALLBACK OWN THE CLASS
-//
-//   MyClass* myclass = new MyClass;
-//   base::Bind(&MyClass::Foo, base::Owned(myclass));
-//
-//   The object will be deleted when the callback is destroyed, even if it's
-//   not run (like if you post a task during shutdown). Potentially useful for
-//   "fire and forget" cases.
-//
-// IGNORING RETURN VALUES
-//
-//   Sometimes you want to call a function that returns a value in a callback
-//   that doesn't expect a return value.
-//
-//   int DoSomething(int arg) { cout << arg << endl; }
-//   base::Callback<void(int)> cb =
-//       base::Bind(base::IgnoreResult(&DoSomething));
-//
-//
-// -----------------------------------------------------------------------------
-// Quick reference for binding parameters to Bind()
-// -----------------------------------------------------------------------------
-//
-// Bound parameters are specified as arguments to Bind() and are passed to the
-// function. A callback with no parameters or no unbound parameters is called a
-// Closure (base::Callback<void()> and base::Closure are the same thing).
-//
-// PASSING PARAMETERS OWNED BY THE CALLBACK
-//
-//   void Foo(int* arg) { cout << *arg << endl; }
-//   int* pn = new int(1);
-//   base::Closure foo_callback = base::Bind(&foo, base::Owned(pn));
-//
-//   The parameter will be deleted when the callback is destroyed, even if it's
-//   not run (like if you post a task during shutdown).
-//
-// PASSING PARAMETERS AS A scoped_ptr
-//
-//   void TakesOwnership(std::unique_ptr<Foo> arg) {}
-//   std::unique_ptr<Foo> f(new Foo);
-//   // f becomes null during the following call.
-//   base::Closure cb = base::Bind(&TakesOwnership, base::Passed(&f));
-//
-//   Ownership of the parameter will be with the callback until the it is run,
-//   when ownership is passed to the callback function. This means the callback
-//   can only be run once. If the callback is never run, it will delete the
-//   object when it's destroyed.
-//
-// PASSING PARAMETERS AS A scoped_refptr
-//
-//   void TakesOneRef(scoped_refptr<Foo> arg) {}
-//   scoped_refptr<Foo> f(new Foo)
-//   base::Closure cb = base::Bind(&TakesOneRef, f);
-//
-//   This should "just work." The closure will take a reference as long as it
-//   is alive, and another reference will be taken for the called function.
-//
-// PASSING PARAMETERS BY REFERENCE
-//
-//   Const references are *copied* unless ConstRef is used. Example:
-//
-//   void foo(const int& arg) { printf("%d %p\n", arg, &arg); }
-//   int n = 1;
-//   base::Closure has_copy = base::Bind(&foo, n);
-//   base::Closure has_ref = base::Bind(&foo, base::ConstRef(n));
-//   n = 2;
-//   foo(n);                        // Prints "2 0xaaaaaaaaaaaa"
-//   has_copy.Run();                // Prints "1 0xbbbbbbbbbbbb"
-//   has_ref.Run();                 // Prints "2 0xaaaaaaaaaaaa"
-//
-//   Normally parameters are copied in the closure. DANGER: ConstRef stores a
-//   const reference instead, referencing the original parameter. This means
-//   that you must ensure the object outlives the callback!
-//
-//
-// -----------------------------------------------------------------------------
-// Implementation notes
-// -----------------------------------------------------------------------------
-//
-// WHERE IS THIS DESIGN FROM:
-//
-// The design Callback and Bind is heavily influenced by C++'s
-// tr1::function/tr1::bind, and by the "Google Callback" system used inside
-// Google.
-//
-//
-// HOW THE IMPLEMENTATION WORKS:
-//
-// There are three main components to the system:
-//   1) The Callback classes.
-//   2) The Bind() functions.
-//   3) The arguments wrappers (e.g., Unretained() and ConstRef()).
-//
-// The Callback classes represent a generic function pointer. Internally,
-// it stores a refcounted piece of state that represents the target function
-// and all its bound parameters.  Each Callback specialization has a templated
-// constructor that takes an BindState<>*.  In the context of the constructor,
-// the static type of this BindState<> pointer uniquely identifies the
-// function it is representing, all its bound parameters, and a Run() method
-// that is capable of invoking the target.
-//
-// Callback's constructor takes the BindState<>* that has the full static type
-// and erases the target function type as well as the types of the bound
-// parameters.  It does this by storing a pointer to the specific Run()
-// function, and upcasting the state of BindState<>* to a
-// BindStateBase*. This is safe as long as this BindStateBase pointer
-// is only used with the stored Run() pointer.
-//
-// To BindState<> objects are created inside the Bind() functions.
-// These functions, along with a set of internal templates, are responsible for
-//
-//  - Unwrapping the function signature into return type, and parameters
-//  - Determining the number of parameters that are bound
-//  - Creating the BindState storing the bound parameters
-//  - Performing compile-time asserts to avoid error-prone behavior
-//  - Returning an Callback<> with an arity matching the number of unbound
-//    parameters and that knows the correct refcounting semantics for the
-//    target object if we are binding a method.
-//
-// The Bind functions do the above using type-inference, and template
-// specializations.
-//
-// By default Bind() will store copies of all bound parameters, and attempt
-// to refcount a target object if the function being bound is a class method.
-// These copies are created even if the function takes parameters as const
-// references. (Binding to non-const references is forbidden, see bind.h.)
-//
-// To change this behavior, we introduce a set of argument wrappers
-// (e.g., Unretained(), and ConstRef()).  These are simple container templates
-// that are passed by value, and wrap a pointer to argument.  See the
-// file-level comment in base/bind_helpers.h for more info.
-//
-// These types are passed to the Unwrap() functions, and the MaybeRefcount()
-// functions respectively to modify the behavior of Bind().  The Unwrap()
-// and MaybeRefcount() functions change behavior by doing partial
-// specialization based on whether or not a parameter is a wrapper type.
-//
-// ConstRef() is similar to tr1::cref.  Unretained() is specific to Chromium.
-//
-//
-// WHY NOT TR1 FUNCTION/BIND?
-//
-// Direct use of tr1::function and tr1::bind was considered, but ultimately
-// rejected because of the number of copy constructors invocations involved
-// in the binding of arguments during construction, and the forwarding of
-// arguments during invocation.  These copies will no longer be an issue in
-// C++0x because C++0x will support rvalue reference allowing for the compiler
-// to avoid these copies.  However, waiting for C++0x is not an option.
-//
-// Measured with valgrind on gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5), the
-// tr1::bind call itself will invoke a non-trivial copy constructor three times
-// for each bound parameter.  Also, each when passing a tr1::function, each
-// bound argument will be copied again.
-//
-// In addition to the copies taken at binding and invocation, copying a
-// tr1::function causes a copy to be made of all the bound parameters and
-// state.
-//
-// Furthermore, in Chromium, it is desirable for the Callback to take a
-// reference on a target object when representing a class method call.  This
-// is not supported by tr1.
-//
-// Lastly, tr1::function and tr1::bind has a more general and flexible API.
-// This includes things like argument reordering by use of
-// tr1::bind::placeholder, support for non-const reference parameters, and some
-// limited amount of subtyping of the tr1::function object (e.g.,
-// tr1::function<int(int)> is convertible to tr1::function<void(int)>).
-//
-// These are not features that are required in Chromium. Some of them, such as
-// allowing for reference parameters, and subtyping of functions, may actually
-// become a source of errors. Removing support for these features actually
-// allows for a simpler implementation, and a terser Currying API.
-//
-//
-// WHY NOT GOOGLE CALLBACKS?
-//
-// The Google callback system also does not support refcounting.  Furthermore,
-// its implementation has a number of strange edge cases with respect to type
-// conversion of its arguments.  In particular, the argument's constness must
-// at times match exactly the function signature, or the type-inference might
-// break.  Given the above, writing a custom solution was easier.
-//
-//
-// MISSING FUNCTIONALITY
-//  - Invoking the return of Bind.  Bind(&foo).Run() does not work;
-//  - Binding arrays to functions that take a non-const pointer.
-//    Example:
-//      void Foo(const char* ptr);
-//      void Bar(char* ptr);
-//      Bind(&Foo, "test");
-//      Bind(&Bar, "test");  // This fails because ptr is not const.
-//
-// If you are thinking of forward declaring Callback in your own header file,
-// please include "base/callback_forward.h" instead.
+// See //docs/callback.md for documentation.
 
 namespace base {
 
-template <typename R, typename... Args, internal::CopyMode copy_mode>
-class Callback<R(Args...), copy_mode>
-    : public internal::CallbackBase<copy_mode> {
+namespace internal {
+
+template <typename CallbackType>
+struct IsOnceCallback : std::false_type {};
+
+template <typename Signature>
+struct IsOnceCallback<OnceCallback<Signature>> : std::true_type {};
+
+// RunMixin provides different variants of `Run()` function to `Callback<>`
+// based on the type of callback.
+template <typename CallbackType>
+class RunMixin;
+
+// Specialization for OnceCallback.
+template <typename R, typename... Args>
+class RunMixin<OnceCallback<R(Args...)>> {
+ private:
+  using CallbackType = OnceCallback<R(Args...)>;
+
+ public:
+  using PolymorphicInvoke = R(*)(internal::BindStateBase*, Args&&...);
+
+  R Run(Args... /* args */) const & {
+    // Note: even though this static_assert will trivially always fail, it
+    // cannot be simply replaced with static_assert(false, ...) because:
+    // - Per [dcl.dcl]/p4, a program is ill-formed if the constant-expression
+    //   argument does not evaluate to true.
+    // - Per [temp.res]/p8, if no valid specialization can be generated for a
+    //   template definition, and that template is not instantiated, the
+    //   template definition is ill-formed, no diagnostic required.
+    // These two clauses, taken together, would allow a conforming C++ compiler
+    // to immediately reject static_assert(false, ...), even inside an
+    // uninstantiated template.
+    static_assert(!IsOnceCallback<CallbackType>::value,
+                  "OnceCallback::Run() may only be invoked on a non-const "
+                  "rvalue, i.e. std::move(callback).Run().");
+  }
+
+  R Run(Args... args) && {
+    // Move the callback instance into a local variable before the invocation,
+    // that ensures the internal state is cleared after the invocation.
+    // It's not safe to touch |this| after the invocation, since running the
+    // bound function may destroy |this|.
+    CallbackType cb = static_cast<CallbackType&&>(*this);
+    PolymorphicInvoke f =
+        reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke());
+    return f(cb.bind_state_.get(), std::forward<Args>(args)...);
+  }
+};
+
+// Specialization for RepeatingCallback.
+template <typename R, typename... Args>
+class RunMixin<RepeatingCallback<R(Args...)>> {
  private:
-  using PolymorphicInvoke = R (*)(internal::BindStateBase*, Args&&...);
+  using CallbackType = RepeatingCallback<R(Args...)>;
+
+ public:
+  using PolymorphicInvoke = R(*)(internal::BindStateBase*, Args&&...);
+
+  R Run(Args... args) const {
+    const CallbackType& cb = static_cast<const CallbackType&>(*this);
+    PolymorphicInvoke f =
+        reinterpret_cast<PolymorphicInvoke>(cb.polymorphic_invoke());
+    return f(cb.bind_state_.get(), std::forward<Args>(args)...);
+  }
+};
+
+template <typename From, typename To>
+struct IsCallbackConvertible : std::false_type {};
+
+template <typename Signature>
+struct IsCallbackConvertible<RepeatingCallback<Signature>,
+                             OnceCallback<Signature>> : std::true_type {};
 
+}  // namespace internal
+
+template <typename R,
+          typename... Args,
+          internal::CopyMode copy_mode,
+          internal::RepeatMode repeat_mode>
+class Callback<R(Args...), copy_mode, repeat_mode>
+    : public internal::CallbackBase<copy_mode>,
+      public internal::RunMixin<Callback<R(Args...), copy_mode, repeat_mode>> {
  public:
-  // MSVC 2013 doesn't support Type Alias of function types.
-  // Revisit this after we update it to newer version.
-  typedef R RunType(Args...);
+  static_assert(repeat_mode != internal::RepeatMode::Once ||
+                copy_mode == internal::CopyMode::MoveOnly,
+                "OnceCallback must be MoveOnly.");
+
+  using RunType = R(Args...);
 
   Callback() : internal::CallbackBase<copy_mode>(nullptr) {}
 
-  Callback(internal::BindStateBase* bind_state,
-           PolymorphicInvoke invoke_func)
+  explicit Callback(internal::BindStateBase* bind_state)
       : internal::CallbackBase<copy_mode>(bind_state) {
-    using InvokeFuncStorage =
-        typename internal::CallbackBase<copy_mode>::InvokeFuncStorage;
-    this->polymorphic_invoke_ =
-        reinterpret_cast<InvokeFuncStorage>(invoke_func);
+  }
+
+  template <typename OtherCallback,
+            typename = typename std::enable_if<
+                internal::IsCallbackConvertible<OtherCallback, Callback>::value
+            >::type>
+  Callback(OtherCallback other)
+      : internal::CallbackBase<copy_mode>(std::move(other)) {}
+
+  template <typename OtherCallback,
+            typename = typename std::enable_if<
+                internal::IsCallbackConvertible<OtherCallback, Callback>::value
+            >::type>
+  Callback& operator=(OtherCallback other) {
+    static_cast<internal::CallbackBase<copy_mode>&>(*this) = std::move(other);
+    return *this;
   }
 
   bool Equals(const Callback& other) const {
     return this->EqualsInternal(other);
   }
 
-  // Run() makes an extra copy compared to directly calling the bound function
-  // if an argument is passed-by-value and is copyable-but-not-movable:
-  // i.e. below copies CopyableNonMovableType twice.
-  //   void F(CopyableNonMovableType) {}
-  //   Bind(&F).Run(CopyableNonMovableType());
-  //
-  // We can not fully apply Perfect Forwarding idiom to the callchain from
-  // Callback::Run() to the target function. Perfect Forwarding requires
-  // knowing how the caller will pass the arguments. However, the signature of
-  // InvokerType::Run() needs to be fixed in the callback constructor, so Run()
-  // cannot template its arguments based on how it's called.
-  R Run(Args... args) const {
-    PolymorphicInvoke f =
-        reinterpret_cast<PolymorphicInvoke>(this->polymorphic_invoke_);
-    return f(this->bind_state_.get(), std::forward<Args>(args)...);
-  }
+  friend class internal::RunMixin<Callback>;
 };
 
 }  // namespace base