Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/dom/shadow/ShadowRoot.h

 /*
  * Copyright (C) 2011 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 125 matching lines @@
     void addChildShadowRoot();
     void removeChildShadowRoot();
     void invalidateDescendantInsertionPoints();
 
     // ShadowRoots should never be cloned.
     virtual PassRefPtr<Node> cloneNode(bool) OVERRIDE { return nullptr; }
 
     // FIXME: This shouldn't happen. https://bugs.webkit.org/show_bug.cgi?id=88834
     bool isOrphan() const { return !host(); }
 
-    ShadowRoot* m_prev;
-    ShadowRoot* m_next;
+    RawPtrWillBeMember<ShadowRoot> m_prev;
+    RawPtrWillBeMember<ShadowRoot> m_next;
     OwnPtrWillBeMember<ShadowRootRareData> m_shadowRootRareData;
     unsigned m_numberOfStyles : 27;
     unsigned m_type : 1;
     unsigned m_registeredWithParentShadowRoot : 1;
     unsigned m_descendantInsertionPointsIsValid : 1;
 };
 
 inline Element* ShadowRoot::activeElement() const
 {
     return adjustedFocusedElement();
 }
 
 DEFINE_NODE_TYPE_CASTS(ShadowRoot, isShadowRoot());
 DEFINE_TYPE_CASTS(ShadowRoot, TreeScope, treeScope, treeScope->rootNode().isShadowRoot(), treeScope.rootNode().isShadowRoot());
 
 } // namespace
 
 #endif