Make text track and cue wrapper objects dependent on their media element.

Source/core/html/track/TextTrack.cpp

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
  * Copyright (C) 2011, 2012, 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 410 matching lines @@
 const AtomicString& TextTrack::interfaceName() const
 {
     return EventTargetNames::TextTrack;
 }
 
 ExecutionContext* TextTrack::executionContext() const
 {
     return m_document;
 }
 
-HTMLMediaElement* TextTrack::mediaElement()
+HTMLMediaElement* TextTrack::mediaElement() const
 {
     return m_trackList ? m_trackList->owner() : 0;
 }
 
+Node* TextTrack::owner() const
+{
+    return mediaElement();
+}
+
 } // namespace WebCore