Allow muting/unmuting audio through media track API

media/base/renderer.h

Index: media/base/renderer.h
diff --git a/media/base/renderer.h b/media/base/renderer.h
index 89e349a9350d1c44564690a84bdc2391589e78d2..2fb57679659acae17dec522e8e5da27d235b25d9 100644
--- a/media/base/renderer.h
+++ b/media/base/renderer.h
@@ -16,6 +16,7 @@
 
 namespace media {
 
+class DemuxerStream;
 class DemuxerStreamProvider;
 class VideoFrame;
 
@@ -77,6 +78,17 @@ class MEDIA_EXPORT Renderer {
   // Returns whether |this| renders video.
   virtual bool HasVideo() = 0;
 
+  // Notifies renderer that the set of enabled audio streams/tracks has changed.
+  // The input parameter |enabledAudioStreams| might be empty, which means that
+  // all audio tracks should be disabled/muted.
+  virtual void OnEnabledAudioStreamsChanged(
+      const std::vector<const DemuxerStream*>& enabledAudioStreams) {}
+
+  // Notifies renderer that the selected video stream has changed. The input
+  // parameter |selectedVideoStream| can be null, which means video is disabled.
+  virtual void OnSelectedVideoStreamChanged(
+      const DemuxerStream* selectedVideoStream) {}
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Renderer);
 };