Oilpan: Remove guardRef and guardDeref from TreeScope.

Source/core/dom/TreeScope.h

Index: Source/core/dom/TreeScope.h
diff --git a/Source/core/dom/TreeScope.h b/Source/core/dom/TreeScope.h
index d5dc0ccfd9dc5c07e5fb5ed452d7dc8a37fa3aa3..920222838a059a53a092c88857b2ac69b8ddb3a3 100644
--- a/Source/core/dom/TreeScope.h
+++ b/Source/core/dom/TreeScope.h
@@ -102,6 +102,8 @@ public:
 
     IdTargetObserverRegistry& idTargetObserverRegistry() const { return *m_idTargetObserverRegistry.get(); }
 
+
+#if !ENABLE(OILPAN)
     // Nodes belonging to this scope hold guard references -
     // these are enough to keep the scope from being destroyed, but
     // not enough to keep it from removing its children. This allows a
@@ -137,6 +139,7 @@ public:
         }
 #endif
     }
+#endif
 
     void removedLastRefToScope();
 
@@ -153,6 +156,8 @@ public:
 
     Element* getElementByAccessKey(const String& key) const;
 
+    virtual void trace(Visitor*);
+
 protected:
     TreeScope(ContainerNode&, Document&);
     TreeScope(Document&);
@@ -182,7 +187,7 @@ private:
 
     Node& m_rootNode;
     Document* m_document;
-    TreeScope* m_parentTreeScope;
+    RawPtrWillBeMember<TreeScope> m_parentTreeScope;
     int m_guardRefCount;
 
     OwnPtr<DocumentOrderedMap> m_elementsById;