Oilpan: tidy up reference to the Document's "CSS target".

Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 1272 matching lines @@
     String m_title;
     String m_rawTitle;
     bool m_titleSetExplicitly;
     RefPtrWillBeMember<Element> m_titleElement;
 
     OwnPtr<AXObjectCache> m_axObjectCache;
     OwnPtrWillBeMember<DocumentMarkerController> m_markers;
 
     Timer<Document> m_updateFocusAppearanceTimer;
 
-    Element* m_cssTarget;
+    RawPtrWillBeMember<Element> m_cssTarget;
 
     LoadEventProgress m_loadEventProgress;
 
     double m_startTime;
 
     OwnPtrWillBeMember<ScriptRunner> m_scriptRunner;
 
     WillBeHeapVector<RefPtrWillBeMember<HTMLScriptElement> > m_currentScriptStack;
 
     OwnPtr<TransformSource> m_transformSource;
@@ skipping 152 matching lines @@
 inline bool Node::isDocumentNode() const
 {
     return this == document();
 }
 
 Node* eventTargetNodeForDocument(Document*);
 
 } // namespace WebCore
 
 #endif // Document_h