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

Source/core/html/HTMLFormElement.idl

 /*
  * Copyright (C) 2006, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 15 matching lines @@
     [Reflect, ReflectOnly="on"|"off", ReflectMissing="on", ReflectInvalid="on"] attribute DOMString autocomplete;
     [CustomElementCallbacks] attribute DOMString enctype;
     [CustomElementCallbacks] attribute DOMString encoding;
     [CustomElementCallbacks] attribute DOMString method;
     [Reflect] attribute DOMString name;
     [Reflect] attribute boolean noValidate;
     [Reflect] attribute DOMString target;
 
     readonly attribute HTMLCollection elements;
     readonly attribute long length;
-    [ImplementedAs=item] getter Node (unsigned long index);
+    [ImplementedAs=item] getter Element (unsigned long index);
     [NotEnumerable] getter (RadioNodeList or Element) (DOMString name);
 
     [ImplementedAs=submitFromJavaScript, PerWorldBindings, ActivityLogging=SetterForIsolatedWorlds] void submit();
     [CustomElementCallbacks] void reset();
     boolean checkValidity();
 
     [RuntimeEnabled=RequestAutocomplete] void requestAutocomplete();
     [RuntimeEnabled=RequestAutocomplete] attribute EventHandler onautocomplete;
     [RuntimeEnabled=RequestAutocomplete] attribute EventHandler onautocompleteerror;
 };