Add thread safety to AudioManagerBase to protect access to the audio thread member variable.

media/audio/audio_output_controller.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_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 236 matching lines @@
   base::Lock lock_;
 
   media::SeekableBuffer buffer_;
 
   bool pending_request_;
 
   // SyncReader is used only in low latency mode for synchronous reading.
   SyncReader* sync_reader_;
 
   // The message loop of audio thread that this object runs on.
-  MessageLoop* message_loop_;
+  scoped_refptr<base::MessageLoopProxy> message_loop_;
 
   // When starting stream we wait for data to become available.
   // Number of times left.
   int number_polling_attempts_left_;
 
   // Used to post delayed tasks to ourselves that we can cancel.
   // We don't want the tasks to hold onto a reference as it will slow down
   // shutdown and force it to wait for the most delayed task.
   // Also, if we're shutting down, we do not want to poll for more data.
   base::WeakPtrFactory<AudioOutputController> weak_this_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_