Oilpan: make DocumentFragment a heap allocated object.

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

 /*
  * 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 75 matching lines @@
     void setSize(int, ExceptionState&);
 
     const String& align() const;
     void setAlign(const String&);
 
     const String& text() const { return m_text; }
     void setText(const String&);
 
     void parseSettings(const String&);
 
-    PassRefPtr<DocumentFragment> getCueAsHTML();
-    PassRefPtr<DocumentFragment> createCueRenderingTree();
+    PassRefPtrWillBeRawPtr<DocumentFragment> getCueAsHTML();
+    PassRefPtrWillBeRawPtr<DocumentFragment> createCueRenderingTree();
 
     const String& regionId() const { return m_regionId; }
     void setRegionId(const String&);
 
     virtual void updateDisplay(const IntSize& videoSize, HTMLDivElement& container) OVERRIDE;
 
     virtual void updateDisplayTree(double movieTime) OVERRIDE;
     virtual void removeDisplayTree() OVERRIDE;
     virtual void notifyRegionWhenRemovingDisplayTree(bool notifyRegion) OVERRIDE;
 
@@ skipping 83 matching lines @@
     bool m_displayTreeShouldChange : 1;
     bool m_notifyRegion : 1;
 };
 
 // VTTCue is currently the only TextTrackCue subclass.
 DEFINE_TYPE_CASTS(VTTCue, TextTrackCue, cue, true, true);
 
 } // namespace WebCore
 
 #endif