Use the browser UI thread for audio on OSX.

media/audio/audio_manager.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_MANAGER_H_
 #define MEDIA_AUDIO_AUDIO_MANAGER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 94 matching lines @@
   // When you are done with it, call |Stop()| and |Close()| to release it.
   virtual AudioInputStream* MakeAudioInputStream(
       const AudioParameters& params, const std::string& device_id) = 0;
 
   // Used to determine if something else is currently making use of audio input.
   virtual bool IsRecordingInProcess() = 0;
 
   // Returns message loop used for audio IO.
   virtual scoped_refptr<base::MessageLoopProxy> GetMessageLoop() = 0;
 
+  // Heavyweight tasks should use GetWorkerLoop() instead of GetMessageLoop().
+  // On most platforms they are the same, but some share the UI loop with the
+  // audio IO loop.
+  virtual scoped_refptr<base::MessageLoopProxy> GetWorkerLoop() = 0;
+
   // Allows clients to listen for device state changes; e.g. preferred sample
   // rate or channel layout changes.  The typical response to receiving this
   // callback is to recreate the stream.
   class AudioDeviceListener {
    public:
     virtual void OnDeviceChange() = 0;
   };
 
   virtual void AddOutputDeviceChangeListener(AudioDeviceListener* listener) = 0;
   virtual void RemoveOutputDeviceChangeListener(
@@ skipping 14 matching lines @@
  protected:
   AudioManager();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(AudioManager);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_MANAGER_H_