Move OnDecoderInitDone() from decoder to pipeline thread.

media/audio/null_audio_sink.h

Index: media/audio/null_audio_sink.h
diff --git a/media/audio/null_audio_sink.h b/media/audio/null_audio_sink.h
index c528473fc91b1913192f3248b7c206fdd70ff30b..fbfb7ffaf93a8bf1c2090b4d031b2e49ba71fb34 100644
--- a/media/audio/null_audio_sink.h
+++ b/media/audio/null_audio_sink.h
@@ -50,8 +50,6 @@ class MEDIA_EXPORT NullAudioSink
   // audio data.
   void FillBufferTask();
 
-  void SetPlaying(bool is_playing);
-
   // A buffer passed to FillBuffer to advance playback.
   scoped_ptr<AudioBus> audio_bus_;
 
@@ -62,7 +60,6 @@ class MEDIA_EXPORT NullAudioSink
 
   // Separate thread used to throw away data.
   base::Thread thread_;
-  base::Lock lock_;
 
   // Controls whether or not a running MD5 hash is computed for audio frames.
   bool hash_audio_for_testing_;