Remove unnecessary lock in AOC; use atomic ref count instead.

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 <stdint.h>
 #include <memory>
 #include <set>
@@ skipping 216 matching lines @@
 
   // Specifies the device id of the output device to open or empty for the
   // default output device.
   std::string output_device_id_;
 
   AudioOutputStream* stream_;
 
   // When non-NULL, audio is being diverted to this stream.
   AudioOutputStream* diverting_to_stream_;
 
-  // The targets for audio stream to be copied to.
+  // The targets for audio stream to be copied to. |should_duplicate_| is set to
+  // 1 when the OnMoreData() call should proxy the data to
+  // BroadcastDataToDuplicationTargets().
   std::set<AudioPushSink*> duplication_targets_;
-  base::Lock duplication_targets_lock_;
+  base::AtomicRefCount should_duplicate_;
 
   // The current volume of the audio stream.
   double volume_;
 
   // |state_| may only be used on the audio manager thread.
   State state_;
 
   // SyncReader is used only in low latency mode for synchronous reading.
   SyncReader* const sync_reader_;
 
@@ skipping 16 matching lines @@
   // be accessed while |error_lock_| is held.
   bool ignore_errors_during_stop_close_;
   base::Lock error_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_