Introduce toHTMLFormControlElement, and use it.

Source/core/html/HTMLFieldSetElement.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, 2010 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 36 matching lines @@
 
 PassRefPtr<HTMLFieldSetElement> HTMLFieldSetElement::create(const QualifiedName& tagName, Document* document, HTMLFormElement* form)
 {
     return adoptRef(new HTMLFieldSetElement(tagName, document, form));
 }
 
 void HTMLFieldSetElement::invalidateDisabledStateUnder(Element* base)
 {
     for (Element* element = ElementTraversal::firstWithin(base); element; element = ElementTraversal::next(element, base)) {
         if (element->isFormControlElement())
-            static_cast<HTMLFormControlElement*>(element)->ancestorDisabledStateWasChanged();
+            toHTMLFormControlElement(element)->ancestorDisabledStateWasChanged();
     }
 }
 
 void HTMLFieldSetElement::disabledAttributeChanged()
 {
     // This element must be updated before the style of nodes in its subtree gets recalculated.
     HTMLFormControlElement::disabledAttributeChanged();
     invalidateDisabledStateUnder(this);
 }
 
@@ skipping 48 matching lines @@
 
     for (Element* element = ElementTraversal::firstWithin(this); element; element = ElementTraversal::next(element, this)) {
         if (element->hasTagName(objectTag)) {
             m_associatedElements.append(static_cast<HTMLObjectElement*>(element));
             continue;
         }
 
         if (!element->isFormControlElement())
             continue;
 
-        m_associatedElements.append(static_cast<HTMLFormControlElement*>(element));
+        m_associatedElements.append(toHTMLFormControlElement(element));
     }
 }
 
 const Vector<FormAssociatedElement*>& HTMLFieldSetElement::associatedElements() const
 {
     refreshElementsIfNeeded();
     return m_associatedElements;
 }
 
 unsigned HTMLFieldSetElement::length() const
 {
     refreshElementsIfNeeded();
     unsigned len = 0;
     for (unsigned i = 0; i < m_associatedElements.size(); ++i)
         if (m_associatedElements[i]->isEnumeratable())
             ++len;
     return len;
 }
 
 } // namespace