Migrates battery_status from content/renderer/ to WebKit/platform/

third_party/WebKit/Source/platform/base/Bind.h

+// Copyright 2016 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.
+
+#ifndef Bind_h
+#define Bind_h
+
+#include "base/bind.h"
+
+// This file provides limited access to base::Bind() function. base::Bind()
+// could be dangerous if it's used across threads, so we don't want to allow
+// general use of base::Bind().
+// See also "platform/ThreadSafeFunctional.h".
+
+namespace blink {
+
+// Binds an instance of a class to its member function. Does not bind anything
+// else.
+template<typename Class, typename ReturnType, typename... Args>
+auto bindInstanceToMethod(ReturnType (Class::*method)(Args...), Class* instance)

[dcheng, 2016/01/27 02:50:01]

Out of curiosity, why not base::Callback<ReturnType(Args...)>
bindInstanceToMethod(...)?

[Yuki, 2016/01/27 04:29:45]

The return type of base::Bind is

template <typename Functor, typename... Args>
base::Callback<
    typename internal::BindState<
        typename internal::FunctorTraits<Functor>::RunnableType,
        typename internal::FunctorTraits<Functor>::RunType,
        typename internal::CallbackParamTraits<Args>::StorageType...>
            ::UnboundRunType>

and it's really hard to write the completely same type manually here (note that
bindInstanceToMethod and base::Bind take different template parameters), and I
think we shouldn't depend on too much of details of the internal implementation
of Bind.

What we'd like to return is what base::Bind returns.  That's
"decltype(base::Bind(...))".

[tzik, 2016/01/27 05:17:26]

The result of the complex template is just to drop some items from Args.
base::Callback<ReturnType(Args...)> seems to work here.

[Yuki, 2016/01/27 05:31:08]

Ah, I see.  Good to know.  Thanks.

+    -> decltype(base::Bind(method, base::Unretained(instance)))
+{
+    return base::Bind(method, base::Unretained(instance));
+}
+
+} // namespace blink
+
+#endif // Bind_h