Oilpan: Make the Node hierarchy RefCountedGarbageCollected instead of TreeShared.

Source/core/dom/shadow/ElementShadow.h

Index: Source/core/dom/shadow/ElementShadow.h
diff --git a/Source/core/dom/shadow/ElementShadow.h b/Source/core/dom/shadow/ElementShadow.h
index a5538a43c100bc28c7062bafc20530f69e168ab2..a0d61abcc6f2414dffa158daa6a5e447f9386b4b 100644
--- a/Source/core/dom/shadow/ElementShadow.h
+++ b/Source/core/dom/shadow/ElementShadow.h
@@ -39,7 +39,7 @@
 
 namespace WebCore {
 
-class ElementShadow {
+class ElementShadow FINAL {
     WTF_MAKE_NONCOPYABLE(ElementShadow); WTF_MAKE_FAST_ALLOCATED;
 public:
     static PassOwnPtr<ElementShadow> create();
@@ -69,6 +69,8 @@ public:
 
     void didDistributeNode(const Node*, InsertionPoint*);
 
+    void trace(Visitor*);
+
 private:
     ElementShadow();