media::BindToLoop() is born, with example uses to slim down WebMediaPlayerProxy.

media/base/bind_to_loop.h

Index: media/base/bind_to_loop.h
diff --git a/media/base/bind_to_loop.h b/media/base/bind_to_loop.h
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+// This file was GENERATED by command:
+//     pump.py bind_to_loop.h.pump
+// DO NOT EDIT BY HAND!!!
+
+
+// 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.
+
+#ifndef MEDIA_BASE_BIND_TO_LOOP_H_
+#define MEDIA_BASE_BIND_TO_LOOP_H_
+
+#include "base/bind.h"
+#include "base/callback_internal.h" // Avoid re-inventing CallbackForward.
+#include "base/location.h"
+#include "base/message_loop_proxy.h"
+
+// This is a helper utility for base::Bind()ing callbacks on to particular
+// MessageLoops.  A typical use is when |a| (of class |A|) wants to hand a
+// callback such as base::Bind(&A::AMethod, a) to |b|, but needs to ensure that
+// when |b| executes the callback, it does so on a particular MessageLoop.
+//
+// Typical usage: request to be called back on the current thread:
+// other->StartAsyncProcessAndCallMeBack(
+//    media::BindToLoop(MessageLoopProxy::current(),
+//                      base::Bind(&MyClass::MyMethod, this)));
+//
+// Note that like base::Bind(), BindToLoop() can't bind non-constant references,
+// and that *unlike* base::Bind(), BindToLoop() makes copies of its arguments,
+// and thus can't be used with arrays.
+
+namespace media {
+
+template <typename T> struct TrampolineHelper;
+
+template <>
+struct TrampolineHelper<void()> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void()>& cb) {
+    loop->PostTask(FROM_HERE, base::Bind(cb));
+  }
+};
+
+
+template <typename A1>
+struct TrampolineHelper<void(A1)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1)>& cb, A1 a1) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1)));
+  }
+};
+
+
+template <typename A1, typename A2>
+struct TrampolineHelper<void(A1, A2)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1, A2)>& cb, A1 a1, A2 a2) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1),
+        base::internal::CallbackForward(a2)));
+  }
+};
+
+
+template <typename A1, typename A2, typename A3>
+struct TrampolineHelper<void(A1, A2, A3)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1, A2, A3)>& cb, A1 a1, A2 a2, A3 a3) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1),
+        base::internal::CallbackForward(a2),
+        base::internal::CallbackForward(a3)));
+  }
+};
+
+
+template <typename A1, typename A2, typename A3, typename A4>
+struct TrampolineHelper<void(A1, A2, A3, A4)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1, A2, A3, A4)>& cb, A1 a1, A2 a2, A3 a3,
+          A4 a4) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1),
+        base::internal::CallbackForward(a2),
+        base::internal::CallbackForward(a3),
+        base::internal::CallbackForward(a4)));
+  }
+};
+
+
+template <typename A1, typename A2, typename A3, typename A4, typename A5>
+struct TrampolineHelper<void(A1, A2, A3, A4, A5)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1, A2, A3, A4, A5)>& cb, A1 a1, A2 a2, A3 a3,
+          A4 a4, A5 a5) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1),
+        base::internal::CallbackForward(a2),
+        base::internal::CallbackForward(a3),
+        base::internal::CallbackForward(a4),
+        base::internal::CallbackForward(a5)));
+  }
+};
+
+
+template <typename A1, typename A2, typename A3, typename A4, typename A5,
+    typename A6>
+struct TrampolineHelper<void(A1, A2, A3, A4, A5, A6)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1, A2, A3, A4, A5, A6)>& cb, A1 a1, A2 a2,
+          A3 a3, A4 a4, A5 a5, A6 a6) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1),
+        base::internal::CallbackForward(a2),
+        base::internal::CallbackForward(a3),
+        base::internal::CallbackForward(a4),
+        base::internal::CallbackForward(a5),
+        base::internal::CallbackForward(a6)));
+  }
+};
+
+
+template <typename A1, typename A2, typename A3, typename A4, typename A5,
+    typename A6, typename A7>
+struct TrampolineHelper<void(A1, A2, A3, A4, A5, A6, A7)> {
+  static void Run(
+      const scoped_refptr<base::MessageLoopProxy>& loop,
+      const base::Callback<void(A1, A2, A3, A4, A5, A6, A7)>& cb, A1 a1, A2 a2,
+          A3 a3, A4 a4, A5 a5, A6 a6, A7 a7) {
+    loop->PostTask(FROM_HERE, base::Bind(cb,
+        base::internal::CallbackForward(a1),
+        base::internal::CallbackForward(a2),
+        base::internal::CallbackForward(a3),
+        base::internal::CallbackForward(a4),
+        base::internal::CallbackForward(a5),
+        base::internal::CallbackForward(a6),
+        base::internal::CallbackForward(a7)));
+  }
+};
+
+
+template<typename T>
+static base::Callback<T> BindToLoop(
+    const scoped_refptr<base::MessageLoopProxy>& loop,
+    const base::Callback<T>& cb) {
+  return base::Bind(&TrampolineHelper<T>::Run, loop, cb);
+}
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_BIND_TO_LOOP_H_