Allow muting/unmuting audio through media track API

media/base/demuxer.h

Index: media/base/demuxer.h
diff --git a/media/base/demuxer.h b/media/base/demuxer.h
index 6e1344bd2cb1ea2440447d7c17ed7a3e457c08fa..83679ce736a18c6529aa321efef5d0c16ed23e6a 100644
--- a/media/base/demuxer.h
+++ b/media/base/demuxer.h
@@ -22,6 +22,7 @@
 namespace media {
 
 class TextTrackConfig;
+class MediaTrack;
 class MediaTracks;
 
 class MEDIA_EXPORT DemuxerHost {
@@ -133,6 +134,16 @@ class MEDIA_EXPORT Demuxer : public DemuxerStreamProvider {
   // Returns the memory usage in bytes for the demuxer.
   virtual int64_t GetMemoryUsage() const = 0;
 
+  // Notifies the demuxer that a track id has been assigned to a media track.

[wolenetz, 2016/03/30 00:31:32]

nit: is this a blink track id? Clarify in comment please.

+  // If |track| is null the association for this |track_id| is removed.
+  virtual void OnTrackIdAssigned(unsigned track_id,

[wolenetz, 2016/03/30 00:31:32]

Question: would these be better in DemuxerHost?

[servolk, 2016/03/30 01:13:12]

Why in DemuxerHost? I was thinking about moving this to DemuxerStreamProvider
instead, to ensure we can support mojo renderers.

+                                 const MediaTrack* track) = 0;
+
+  // Finds a DemuxerStream corresponding to the given blink |track_id|. Note
+  // that the input track id is blink track id and not bytestream track id.
+  virtual const DemuxerStream* GetDemuxerStreamByTrackId(
+      unsigned track_id) const = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Demuxer);
 };