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

Source/core/html/HTMLFormElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 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 36 matching lines @@
 
 class HTMLFormElement FINAL : public HTMLElement {
 public:
     static PassRefPtr<HTMLFormElement> create(Document&);
     virtual ~HTMLFormElement();
 
     PassRefPtr<HTMLCollection> elements();
     void getNamedElements(const AtomicString&, Vector<RefPtr<Element> >&);
 
     unsigned length() const;
-    Node* item(unsigned index);
+    Element* item(unsigned index);
 
     String enctype() const { return m_attributes.encodingType(); }
     void setEnctype(const AtomicString&);
 
     String encoding() const { return m_attributes.encodingType(); }
     void setEncoding(const AtomicString& value) { setEnctype(value); }
 
     bool shouldAutocomplete() const;
 
     void associate(FormAssociatedElement&);
@@ skipping 115 matching lines @@
 
     Vector<RefPtr<Event> > m_pendingAutocompleteEvents;
     Timer<HTMLFormElement> m_requestAutocompleteTimer;
 };
 
 DEFINE_NODE_TYPE_CASTS(HTMLFormElement, hasTagName(HTMLNames::formTag));
 
 } // namespace WebCore
 
 #endif // HTMLFormElement_h