AudioManagerBase: Create and run the audio thread lazily.

media/audio/audio_manager.h

Index: media/audio/audio_manager.h
diff --git a/media/audio/audio_manager.h b/media/audio/audio_manager.h
index c5b7f194d18af55be4f1a8b5b7716b3b4bbdc27f..d3eea4a6b9cdcf5b944e076dc12e983a82109b05 100644
--- a/media/audio/audio_manager.h
+++ b/media/audio/audio_manager.h
@@ -178,7 +178,7 @@ class MEDIA_EXPORT AudioManager {
       const std::string& device_id) = 0;
 
   // Returns the task runner used for audio IO.
-  virtual scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() const = 0;
+  virtual scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() = 0;
 
   // Heavyweight tasks should use GetWorkerTaskRunner() instead of
   // GetTaskRunner(). On most platforms they are the same, but some share the