Allow muting/unmuting audio through media track API

media/filters/chunk_demuxer.h

Index: media/filters/chunk_demuxer.h
diff --git a/media/filters/chunk_demuxer.h b/media/filters/chunk_demuxer.h
index 677fa2a41cff9bee3114f9e7f46872b887899e44..beae244c95b5391edc75ed6d2d289139dfea8f0d 100644
--- a/media/filters/chunk_demuxer.h
+++ b/media/filters/chunk_demuxer.h
@@ -208,6 +208,15 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   void SetTracksWatcher(const std::string& id,
                         const MediaTracksUpdatedCB& tracks_updated_cb);
 
+  // Notifies the demuxer that a track id has been assigned to a media track.
+  // If |track| is null the association for this |track_id| is removed.

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

who owns the memory pointed to by |track|?

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

It doesn't matter, because we don't actually care about the MediaTrack lifetime
here. We don't even need it to be alive! I'm essentially just using the pointer
value as a unique track id here, which will allow us to establish mapping from
blink trackId -> MediaTrack* -> DemuxerStream*. And then we pass the
DemuxerStream* pointer values to media::Renderer. We never access the pointee
objects, so they don't need to be alive. When media::Renderer receives the
DemuxerStream*, it can use it as an identifier that points to some DemuxerStream
and media::Renderer knows about DemuxerStreams, so then the RendererImpl can
check that the given DemuxerStream* pointers are valid and alive.

[wolenetz, 2016/03/30 20:15:55]

Hmm. Using a pointer just as an ID is not clear and risks future incorrect
dereferencing. Please try a better way to identify uniquely the Chromium
MediaTrack in these (persistent) mappings that may survive beyond the life of
the Chromium MediaTrack.

+  void OnTrackIdAssigned(unsigned track_id, const MediaTrack* track) override;
+
+  // 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.
+  const DemuxerStream* GetDemuxerStreamByTrackId(
+      unsigned track_id) const override;
+
   // Removed an ID & associated resources that were previously added with
   // AddId().
   void RemoveId(const std::string& id);
@@ -318,10 +327,10 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   // MediaSourceState callbacks.
   void OnSourceInitDone(const StreamParser::InitParameters& params);
 
-  // Creates a DemuxerStream for the specified |type|.
+  // Creates a DemuxerStream for the specified |media_track|.
   // Returns a new ChunkDemuxerStream instance if a stream of this type
   // has not been created before. Returns NULL otherwise.
-  ChunkDemuxerStream* CreateDemuxerStream(DemuxerStream::Type type);
+  ChunkDemuxerStream* CreateDemuxerStream(const MediaTrack& media_track);
 
   void OnNewTextTrack(ChunkDemuxerStream* text_stream,
                       const TextTrackConfig& config);
@@ -381,6 +390,9 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   scoped_ptr<ChunkDemuxerStream> audio_;
   scoped_ptr<ChunkDemuxerStream> video_;
 
+  std::map<unsigned, const MediaTrack*> track_id_to_track_map_;
+  std::map<const MediaTrack*, const DemuxerStream*> track_to_stream_map_;
+
   base::TimeDelta duration_;
 
   // The duration passed to the last SetDuration(). If