Introduce toHTMLInputElement(Node*), and use it.

Source/WebKit/chromium/src/DOMUtilitiesPrivate.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 25 matching lines @@
 #include "core/html/HTMLInputElement.h"
 
 using namespace WebCore;
 using namespace WebCore::HTMLNames;
 
 namespace WebKit {
 
 bool elementHasLegalLinkAttribute(const Element* element, const QualifiedName& attrName)
 {
     if (attrName == srcAttr)
-        return element->hasTagName(imgTag) || element->hasTagName(scriptTag) || element->hasTagName(iframeTag) || element->hasTagName(frameTag) || (element->hasTagName(inputTag) && static_cast<const HTMLInputElement*>(element)->isImageButton());
+        return element->hasTagName(imgTag) || element->hasTagName(scriptTag) || element->hasTagName(iframeTag) || element->hasTagName(frameTag) || (element->hasTagName(inputTag) && toHTMLInputElement(element)->isImageButton());
     if (attrName == hrefAttr)
         return element->hasTagName(linkTag) || element->hasTagName(aTag) || element->hasTagName(areaTag);
     if (attrName == actionAttr)
         return element->hasTagName(formTag);
     if (attrName == backgroundAttr)
         return element->hasTagName(bodyTag) || element->hasTagName(tableTag) || element->hasTagName(trTag) || element->hasTagName(tdTag);
     if (attrName == citeAttr)
         return element->hasTagName(blockquoteTag) || element->hasTagName(qTag) || element->hasTagName(delTag) || element->hasTagName(insTag);
     if (attrName == classidAttr || attrName == dataAttr)
         return element->hasTagName(objectTag);
     if (attrName == codebaseAttr)
         return element->hasTagName(objectTag) || element->hasTagName(appletTag);
     return false;
 }
 
 } // namespace WebKit