Oilpan: move DOM string collection objects to the Oilpan heap.

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 3278 matching lines @@
         || isHTMLAppletElement(*this)
         || isHTMLCanvasElement(*this))
         return false;
     if (FullscreenElementStack::isActiveFullScreenElement(this))
         return false;
     return true;
 }
 
 void Element::trace(Visitor* visitor)
 {
-    // FIXME: Oilpan: Perform this tracing directly on the element
-    // rare data once that is in the heap.
     if (hasRareData())
-        elementRareData()->trace(visitor);
+        visitor->trace(elementRareData());
+
     ContainerNode::trace(visitor);
 }
 
 } // namespace WebCore