Oilpan: Remove guardRef and guardDeref from TreeScope.

Source/core/page/DOMSelection.h

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2012 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 78 matching lines @@
     void addRange(Range*);
     void deleteFromDocument();
     bool containsNode(const Node*, bool partlyContained) const;
     void selectAllChildren(Node*, ExceptionState&);
 
     String toString();
 
     // Microsoft Selection Object API
     void empty();
 
-    void trace(Visitor*) { }
+    void trace(Visitor* visitor) { visitor->trace(m_treeScope); }
 
 private:
     explicit DOMSelection(const TreeScope*);
 
     // Convenience method for accessors, does not check m_frame present.
     const VisibleSelection& visibleSelection() const;
 
     Node* shadowAdjustedNode(const Position&) const;
     int shadowAdjustedOffset(const Position&) const;
 
     bool isValidForPosition(Node*) const;
 
     void addConsoleError(const String& message);
 
-    const TreeScope* m_treeScope;
+    RawPtrWillBeMember<const TreeScope> m_treeScope;
 };
 
 } // namespace WebCore
 
 #endif // DOMSelection_h