Pass in media message loop to VideoRendererBase and enforce calling on the right thread.

media/base/callback_wrapper.h

+// 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_CALLBACK_WRAPPER_H_
+#define MEDIA_BASE_CALLBACK_WRAPPER_H_
+
+#include "base/callback.h"
+#include "base/message_loop_proxy.h"
+
+// This is a helper utility for running callbacks on the current message loop as
+// a freshly posted task as opposed to executing on the current stack.
+//
+// Typical usage is when implementing an asynchronous callback-accepting
+// interface in a synchronous fashion. Running the callback as a posted task
+// prevents reentrancy into the calling code.
+//
+// void MyClass::DoSomethingAsync(const base::Closure& closure) {
+//   DoWorkSynchronously();
+//   WrapCB(closure).Run();
+// }
+
+namespace media {
+
+namespace internal {
+void RunWrappedCB(

[scherkus (not reviewing), 2012/12/06 21:57:57]

I just realized I was completely mistaken about BindToLoop()!!!

It *does* do a force-post, which means we can replace all of this with a helper
like BindToCurrentLoop()

+    const scoped_refptr<base::MessageLoopProxy>& message_loop,
+    const base::Closure& cb) {
+  message_loop->PostTask(FROM_HERE, cb);
+}
+
+template<typename A1>
+void RunWrappedCBWithArgs(
+    const scoped_refptr<base::MessageLoopProxy>& message_loop,
+    const base::Callback<void(A1)>& cb,
+    A1 a1) {
+  RunWrappedCB(message_loop, base::Bind(cb, a1));
+}
+
+template<typename A1, typename A2>
+void RunWrappedCBWithArgs(
+    const scoped_refptr<base::MessageLoopProxy>& message_loop,
+    const base::Callback<void(A1, A2)>& cb,
+    A1 a1, A2 a2) {
+  RunWrappedCB(message_loop, base::Bind(cb, a1, a2));
+}
+}  // namespace internal
+
+base::Closure WrapCB(const base::Closure& cb) {
+  return base::Bind(
+      &internal::RunWrappedCB,
+      base::MessageLoopProxy::current(), cb);
+}
+
+template<typename A1>
+base::Callback<void(A1)> WrapCB(const base::Callback<void(A1)>& cb) {
+  return base::Bind(
+      &internal::RunWrappedCBWithArgs<A1>,
+      base::MessageLoopProxy::current(), cb);
+}
+
+template<typename A1, typename A2>
+base::Callback<void(A1, A2)> WrapCB(const base::Callback<void(A1, A2)>& cb) {
+  return base::Bind(
+      &internal::RunWrappedCBWithArgs<A1, A2>,
+      base::MessageLoopProxy::current(), cb);
+}
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_CALLBACK_WRAPPER_H_