Add "change" and "removetrack" events to TextTrackList.

Source/core/html/track/TextTrackList.idl

 /*
  * Copyright (C) 2011 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 13 matching lines @@
  */
 
 [
     GenerateVisitDOMWrapper=owner,
     RuntimeEnabled=VideoTrack,
 ] interface TextTrackList : EventTarget {
     readonly attribute unsigned long length;
     getter TextTrack item(unsigned long index);
 
     attribute EventHandler onaddtrack;
+    attribute EventHandler onchange;
+    attribute EventHandler onremovetrack;
 };