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..f5d59776af7fc177e733baffb2b4e77b5c0dbe1b 100644
--- a/media/base/renderer.h
+++ b/media/base/renderer.h
@@ -5,6 +5,8 @@
 #ifndef MEDIA_BASE_RENDERER_H_
 #define MEDIA_BASE_RENDERER_H_
 
+#include <vector>
+
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ -16,6 +18,7 @@
 
 namespace media {
 
+class DemuxerStream;
 class DemuxerStreamProvider;
 class VideoFrame;
 
@@ -77,6 +80,17 @@ 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) {}

[wolenetz, 2016/04/15 23:52:17]

Is there a bug tracking getting mojo and any other users of this default
implementation to instead do "the right thing" and actuate the effect of streams
changing? If not, please file one. Either way, please reference it in TODO here
and in OnSelectedVideoStreamChanged(), below.

+
+  // 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);
 };