Have HTMLCollection::item() return an Element as per specification

Source/core/html/HTMLCollection.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 26 matching lines @@
         OverridesItemAfter,
         DoesNotOverrideItemAfter,
     };
 
     static PassRefPtr<HTMLCollection> create(ContainerNode* base, CollectionType);
     virtual ~HTMLCollection();
     virtual void invalidateCache() const OVERRIDE;
 
     // DOM API
     unsigned length() const { return m_collectionIndexCache.nodeCount(*this); }
-    Node* item(unsigned offset) const { return m_collectionIndexCache.nodeAt(*this, offset); }
+    Element* item(unsigned offset) const { return m_collectionIndexCache.nodeAt(*this, offset); }
     virtual Element* namedItem(const AtomicString& name) const;
 
     // Non-DOM API
     void namedItems(const AtomicString& name, Vector<RefPtr<Element> >&) const;
     bool isEmpty() const { return m_collectionIndexCache.isEmpty(*this); }
     bool hasExactlyOneItem() const { return m_collectionIndexCache.hasExactlyOneNode(*this); }
 
     // CollectionIndexCache API.
     bool canTraverseBackward() const { return !overridesItemAfter(); }
+    Element* itemBefore(const Node* previousItem) const;
     Element* traverseToFirstElement(const ContainerNode& root) const;
-    Element* traverseForwardToOffset(unsigned offset, Node& currentElement, unsigned& currentOffset, const ContainerNode& root) const;
+    Element* traverseForwardToOffset(unsigned offset, Element& currentElement, unsigned& currentOffset, const ContainerNode& root) const;
 
 protected:
     HTMLCollection(ContainerNode* base, CollectionType, ItemAfterOverrideType);
 
     bool overridesItemAfter() const { return m_overridesItemAfter; }
     virtual Element* virtualItemAfter(Element*) const;
 
     virtual void updateNameCache() const;
     bool hasNameCache() const { return m_isNameCacheValid; }
     void setHasNameCache() const { m_isNameCacheValid = true; }
@@ skipping 13 matching lines @@
     {
         m_idCache.clear();
         m_nameCache.clear();
         m_isNameCacheValid = false;
     }
 
     const unsigned m_overridesItemAfter : 1;
     mutable unsigned m_isNameCacheValid : 1;
     mutable NodeCacheMap m_idCache;
     mutable NodeCacheMap m_nameCache;
-    mutable CollectionIndexCache<HTMLCollection> m_collectionIndexCache;
+    mutable CollectionIndexCache<HTMLCollection, Element> m_collectionIndexCache;
 
     friend class LiveNodeListBase;
 };
 
 } // namespace
 
 #endif