Add toHTMLFieldSetElement and toHTMLLegendElement, and use them.

Source/core/html/HTMLFormControlElement.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 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 88 matching lines @@
 }
 
 void HTMLFormControlElement::updateAncestorDisabledState() const
 {
     HTMLFieldSetElement* fieldSetAncestor = 0;
     ContainerNode* legendAncestor = 0;
     for (ContainerNode* ancestor = parentNode(); ancestor; ancestor = ancestor->parentNode()) {
         if (!legendAncestor && ancestor->hasTagName(legendTag))
             legendAncestor = ancestor;
         if (ancestor->hasTagName(fieldsetTag)) {
-            fieldSetAncestor = static_cast<HTMLFieldSetElement*>(ancestor);
+            fieldSetAncestor = toHTMLFieldSetElement(ancestor);
             break;
         }
     }
     m_ancestorDisabledState = (fieldSetAncestor && fieldSetAncestor->isDisabledFormControl() && !(legendAncestor && legendAncestor == fieldSetAncestor->legend())) ? AncestorDisabledStateDisabled : AncestorDisabledStateEnabled;
 }
 
 void HTMLFormControlElement::ancestorDisabledStateWasChanged()
 {
     m_ancestorDisabledState = AncestorDisabledStateUnknown;
     disabledAttributeChanged();
@@ skipping 374 matching lines @@
 HTMLFormControlElement* HTMLFormControlElement::enclosingFormControlElement(Node* node)
 {
     for (; node; node = node->parentNode()) {
         if (node->isElementNode() && toElement(node)->isFormControlElement())
             return toHTMLFormControlElement(node);
     }
     return 0;
 }
 
 } // namespace Webcore