Generate and assign media track ids in demuxers.

third_party/WebKit/public/platform/WebMediaPlayer.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 84 matching lines @@
     };
 
     // Reported to UMA. Do not change existing values.
     enum LoadType {
         LoadTypeURL = 0,
         LoadTypeMediaSource = 1,
         LoadTypeMediaStream = 2,
         LoadTypeMax = LoadTypeMediaStream,
     };
 
-    typedef unsigned TrackId;
+    typedef WebString TrackId;
     enum TrackType { TextTrack, AudioTrack, VideoTrack };
 
     virtual ~WebMediaPlayer() { }
 
     virtual void load(LoadType, const WebMediaPlayerSource&, CORSMode) = 0;
 
     // Playback controls.
     virtual void play() = 0;
     virtual void pause() = 0;
     virtual bool supportsSave() const = 0;
@@ skipping 82 matching lines @@
     virtual void exitedFullscreen() { }
 
     virtual void enabledAudioTracksChanged(const WebVector<TrackId>& enabledTrackIds) { }
     // |selectedTrackId| is null if no track is selected.
     virtual void selectedVideoTrackChanged(TrackId* selectedTrackId) { }
 };
 
 } // namespace blink
 
 #endif