Oilpan: add transition types to track interface objects.

Source/core/html/track/vtt/VTTCue.cpp

 /*
  * Copyright (c) 2013, Opera Software ASA. 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 1057 matching lines @@
     ASSERT(m_cueBackgroundBox);
     return m_cueBackgroundBox->executionContext();
 }
 
 Document& VTTCue::document() const
 {
     ASSERT(m_cueBackgroundBox);
     return m_cueBackgroundBox->document();
 }
 
+void VTTCue::trace(Visitor* visitor)
+{
+    TextTrackCue::trace(visitor);
+}
+
 } // namespace WebCore