[chromecast] Start deprecating MediaMessageLoop.

chromecast/media/base/media_message_loop.h

 // Copyright 2014 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 CHROMECAST_MEDIA_BASE_MEDIA_MESSAGE_LOOP_H_
 #define CHROMECAST_MEDIA_BASE_MEDIA_MESSAGE_LOOP_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/singleton.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 class Thread;
 }
 
 namespace chromecast {
 namespace media {
 
+// DEPRECATED: This is being deprecated.
+// Get the media task runner from CastContentBrowserClient::GetMediaTaskRunner.
 class MediaMessageLoop {
  public:
   static scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner();
 
   static MediaMessageLoop* GetInstance();
 
  private:
   friend struct base::DefaultSingletonTraits<MediaMessageLoop>;
 
   MediaMessageLoop();
   ~MediaMessageLoop();
 
   scoped_ptr<base::Thread> thread_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaMessageLoop);
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_BASE_MEDIA_MESSAGE_LOOP_H_