Move some Element specific code from Node::detach to Element::detach.

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 593 matching lines @@
     void setNeedsFocusedElementCheck();
     void setAutofocusElement(Element*);
     Element* autofocusElement() const { return m_autofocusElement.get(); }
 
     void setActiveHoverElement(PassRefPtrWillBeRawPtr<Element>);
     Element* activeHoverElement() const { return m_activeHoverElement.get(); }
 
     Node* hoverNode() const { return m_hoverNode.get(); }
 
     void removeFocusedElementOfSubtree(Node*, bool amongChildrenOnly = false);
-    void hoveredNodeDetached(Node*);
-    void activeChainNodeDetached(Node*);
+    void hoveredNodeDetached(Element&);
+    void activeChainNodeDetached(Element&);
 
     void updateHoverActiveState(const HitTestRequest&, Element*);
 
     // Updates for :target (CSS3 selector).
     void setCSSTarget(Element*);
     Element* cssTarget() const { return m_cssTarget; }
 
     void scheduleLayoutTreeUpdateIfNeeded();
     bool hasPendingForcedStyleRecalc() const;
 
@@ skipping 816 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h