Allow muting/unmuting audio through media track API

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index b89196d4a940866fe551a193ceb2aeea51550f51..197cbfde6e6cd83c67b0808a3cc4d5ca2b887ef3 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -25,6 +25,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <map>
 #include <string>
 #include <utility>
 #include <vector>
@@ -223,6 +224,15 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
   // timeline.
   base::TimeDelta start_time() const { return start_time_; }
 
+  // Notifies the demuxer that track ids has been assigned to a media tracks.
+  void OnTrackIdsAssigned(const MediaTracks& tracks,
+                          const std::vector<unsigned>& track_ids) 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;
+
  private:
   // To allow tests access to privates.
   friend class FFmpegDemuxerTest;
@@ -334,6 +344,8 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
 
   const MediaTracksUpdatedCB media_tracks_updated_cb_;
 
+  std::map<unsigned, const DemuxerStream*> track_id_to_demux_stream_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<FFmpegDemuxer> weak_factory_;