Make it obvious an HTMLFormControlsCollection can only contain HTMLElements

Source/core/html/HTMLFormElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.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
@@ skipping 203 matching lines @@
 {
     const FormAssociatedElement::List& elements = associatedElements();
     unsigned len = 0;
     for (unsigned i = 0; i < elements.size(); ++i) {
         if (elements[i]->isEnumeratable())
             ++len;
     }
     return len;
 }
 
-Element* HTMLFormElement::item(unsigned index)
+HTMLElement* HTMLFormElement::item(unsigned index)
 {
     return elements()->item(index);
 }
 
 void HTMLFormElement::submitImplicitly(Event* event, bool fromImplicitSubmissionTrigger)
 {
     int submissionTriggerCount = 0;
     bool seenDefaultButton = false;
     const FormAssociatedElement::List& elements = associatedElements();
     for (unsigned i = 0; i < elements.size(); ++i) {
@@ skipping 610 matching lines @@
 }
 
 void HTMLFormElement::setDemoted(bool demoted)
 {
     if (demoted)
         UseCounter::count(document(), UseCounter::DemotedFormElement);
     m_wasDemoted = demoted;
 }
 
 } // namespace