Implement mapping blink track id to demuxer streams

media/base/media_tracks.h

Index: media/base/media_tracks.h
diff --git a/media/base/media_tracks.h b/media/base/media_tracks.h
index ea4a38c18d8bbb3dc05dcee23c5ee82966eb97f0..1769e61a592142945b5329d79613317c735a11ce 100644
--- a/media/base/media_tracks.h
+++ b/media/base/media_tracks.h
@@ -17,30 +17,47 @@
 namespace media {
 
 class AudioDecoderConfig;
+class DemuxerStream;
 class VideoDecoderConfig;
 
 class MEDIA_EXPORT MediaTracks {
  public:
   using MediaTracksCollection = std::vector<std::unique_ptr<MediaTrack>>;
+  using TrackIdToDemuxStreamMap = std::map<unsigned, const DemuxerStream*>;
 
   MediaTracks();
   ~MediaTracks();
 
   // Callers need to ensure that track id is unique.
-  void AddAudioTrack(const AudioDecoderConfig& config,
-                     const std::string& id,
-                     const std::string& kind,
-                     const std::string& label,
-                     const std::string& language);
+  const MediaTrack* AddAudioTrack(const AudioDecoderConfig& config,
+                                  const std::string& id,
+                                  const std::string& kind,
+                                  const std::string& label,
+                                  const std::string& language);
   // Callers need to ensure that track id is unique.
-  void AddVideoTrack(const VideoDecoderConfig& config,
-                     const std::string& id,
-                     const std::string& kind,
-                     const std::string& label,
-                     const std::string& language);
+  const MediaTrack* AddVideoTrack(const VideoDecoderConfig& config,
+                                  const std::string& id,
+                                  const std::string& kind,
+                                  const std::string& label,
+                                  const std::string& language);
 
   const MediaTracksCollection& tracks() const { return tracks_; }
 
+  // TODO(servolk,wolenetz): Consider refactoring media track creation in MSE to
+  // simplify track id to DemuxerStream mapping. crbug.com/604088
+
+  // Notifies MediaTracks that a given media |track| object is backed by the
+  // given DemuxerStream |stream| object.
+  void SetDemuxerStreamForMediaTrack(const MediaTrack* track,
+                                     const DemuxerStream* stream);
+  // Notifies MediaTracks that external (blink) track ids have been assigned to
+  // the media |tracks_|. The size and ordering of |track_ids| must match the
+  // size and ordering of tracks in the |tracks_| collection, and
+  // |track_to_demux_stream_map_| must have an entry for each track in |tracks_|
+  // (set by SetDemuxerStreamForMediaTrack()).
+  TrackIdToDemuxStreamMap OnTrackIdsAssigned(
+      const std::vector<unsigned>& track_ids) const;
+
   const AudioDecoderConfig& getAudioConfig(const std::string& id) const;
   const VideoDecoderConfig& getVideoConfig(const std::string& id) const;
 
@@ -54,6 +71,10 @@ class MEDIA_EXPORT MediaTracks {
   std::map<std::string, AudioDecoderConfig> audio_configs_;
   std::map<std::string, VideoDecoderConfig> video_configs_;
 
+  using TrackToDemuxStreamMap =
+      std::map<const MediaTrack*, const DemuxerStream*>;
+  TrackToDemuxStreamMap track_to_demux_stream_map_;
+
   DISALLOW_COPY_AND_ASSIGN(MediaTracks);
 };