[chromecast] Simplify CastAudioOutputStream.

chromecast/media/audio/cast_audio_manager.h

Index: chromecast/media/audio/cast_audio_manager.h
diff --git a/chromecast/media/audio/cast_audio_manager.h b/chromecast/media/audio/cast_audio_manager.h
index 572b99fe6b6fc4e155bf0c1a1bb9d47a7d319b01..213e52c82a595d42b5205d561a0e32a11c2c2634 100644
--- a/chromecast/media/audio/cast_audio_manager.h
+++ b/chromecast/media/audio/cast_audio_manager.h
@@ -35,8 +35,7 @@ class CastAudioManager : public ::media::AudioManagerBase {
   ::media::AudioParameters GetInputStreamParameters(
       const std::string& device_id) override;
 
-  // This must be called on cast media thread.
-  // See chromecast::media::MediaMessageLoop.
+  // This must be called on audio thread.
   virtual std::unique_ptr<MediaPipelineBackend> CreateMediaPipelineBackend(
       const MediaPipelineDeviceParams& params);