Implement AudioTrack, AudioTrackList, VideoTrack, and VideoTrackList

public/platform/WebMediaPlayer.h

Index: public/platform/WebMediaPlayer.h
diff --git a/public/platform/WebMediaPlayer.h b/public/platform/WebMediaPlayer.h
index 734f7c2b37b1d73aef0465933101235c9cc60a91..9915b55a10b1907c921b33b14a6e26c474fffd2a 100644
--- a/public/platform/WebMediaPlayer.h
+++ b/public/platform/WebMediaPlayer.h
@@ -48,6 +48,8 @@ struct WebRect;
 struct WebSize;
 class WebGraphicsContext3D;
 
+typedef unsigned WebTrackId;
+
 class WebMediaPlayer {
 public:
     enum NetworkState {
@@ -162,6 +164,9 @@ public:
     virtual void exitFullscreen() { }
     // Returns true if the player can enter fullscreen.
     virtual bool canEnterFullscreen() const { return false; }
+
+    virtual void enabledAudioTracksChanged(const WebVector<WebTrackId>& enabledTrackIds) { }
+    virtual void selectedVideoTrackChanged(WebTrackId* selectedTrackId) { }
 };
 
 } // namespace blink