Generate and assign media track ids in demuxers.

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 be0f9dbc38be5283202b297eb17167414d6be383..9dfc1ecb0c0a1bed5d8f498ec85a3d1eb71b9383 100644
--- a/media/filters/chunk_demuxer.h
+++ b/media/filters/chunk_demuxer.h
@@ -19,6 +19,7 @@
 #include "media/base/byte_queue.h"
 #include "media/base/demuxer.h"
 #include "media/base/demuxer_stream.h"
+#include "media/base/media_tracks.h"
 #include "media/base/ranges.h"
 #include "media/base/stream_parser.h"
 #include "media/filters/media_source_state.h"
@@ -32,7 +33,9 @@ class MEDIA_EXPORT ChunkDemuxerStream : public DemuxerStream {
  public:
   typedef std::deque<scoped_refptr<StreamParserBuffer> > BufferQueue;
 
-  ChunkDemuxerStream(Type type, bool splice_frames_enabled);
+  ChunkDemuxerStream(Type type,
+                     bool splice_frames_enabled,
+                     MediaTrack::Id media_track_id);
   ~ChunkDemuxerStream() override;
 
   // ChunkDemuxerStream control methods.
@@ -118,6 +121,8 @@ class MEDIA_EXPORT ChunkDemuxerStream : public DemuxerStream {
 
   void SetLiveness(Liveness liveness);
 
+  MediaTrack::Id media_track_id() const { return media_track_id_; }
+
  private:
   enum State {
     UNINITIALIZED,
@@ -138,6 +143,8 @@ class MEDIA_EXPORT ChunkDemuxerStream : public DemuxerStream {
 
   std::unique_ptr<SourceBufferStream> stream_;
 
+  const MediaTrack::Id media_track_id_;
+
   mutable base::Lock lock_;
   State state_;
   ReadCB read_cb_;
@@ -355,6 +362,9 @@ class MEDIA_EXPORT ChunkDemuxer : public Demuxer {
   // Seeks all SourceBufferStreams to |seek_time|.
   void SeekAllSources(base::TimeDelta seek_time);
 
+  // Generates and returns a unique media track id.
+  static MediaTrack::Id GenerateMediaTrackId();
+
   // Shuts down all DemuxerStreams by calling Shutdown() on
   // all objects in |source_state_map_|.
   void ShutdownAllStreams();