Introduce toHTMLFormControlElement, and use it.

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 444 matching lines @@
 
 bool HTMLFormControlElement::isDefaultButtonForForm() const
 {
     return isSuccessfulSubmitButton() && form() && form()->defaultButton() == this;
 }
 
 HTMLFormControlElement* HTMLFormControlElement::enclosingFormControlElement(Node* node)
 {
     for (; node; node = node->parentNode()) {
         if (node->isElementNode() && toElement(node)->isFormControlElement())
-            return static_cast<HTMLFormControlElement*>(node);
+            return toHTMLFormControlElement(node);
     }
     return 0;
 }
 
 void HTMLFormControlElement::reportMemoryUsage(MemoryObjectInfo* memoryObjectInfo) const
 {
     MemoryClassInfo info(memoryObjectInfo, this, WebCoreMemoryTypes::DOM);
     LabelableElement::reportMemoryUsage(memoryObjectInfo);
     info.addMember(m_validationMessage, "validationMessage");
 }
 
 } // namespace Webcore