Oilpan: add transition types to track interface objects.

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

 /*
  * Copyright (C) 2013 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 70 matching lines @@
     return false;
 }
 
 VTTRegion::VTTRegion()
     : m_id(emptyString())
     , m_width(defaultWidth)
     , m_heightInLines(defaultHeightInLines)
     , m_regionAnchor(FloatPoint(defaultAnchorPointX, defaultAnchorPointY))
     , m_viewportAnchor(FloatPoint(defaultAnchorPointX, defaultAnchorPointY))
     , m_scroll(defaultScroll)
-    , m_track(0)
+    , m_track(nullptr)
     , m_currentTop(0)
     , m_scrollTimer(this, &VTTRegion::scrollTimerFired)
 {
 }
 
 VTTRegion::~VTTRegion()
 {
 }
 
 void VTTRegion::setTrack(TextTrack* track)
@@ skipping 362 matching lines @@
 }
 
 void VTTRegion::scrollTimerFired(Timer<VTTRegion>*)
 {
     WTF_LOG(Media, "VTTRegion::scrollTimerFired");
 
     stopTimer();
     displayLastVTTCueBox();
 }
 
+void VTTRegion::trace(Visitor* visitor)
+{
+    visitor->trace(m_track);
+}
+
 } // namespace WebCore