Add const versions of some toHTMLFooElement().

Source/core/html/FormAssociatedElement.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 259 matching lines @@
 }
 
 bool FormAssociatedElement::isFormControlElementWithState() const
 {
     return false;
 }
 
 const HTMLElement* toHTMLElement(const FormAssociatedElement* associatedElement)
 {
     if (associatedElement->isFormControlElement())
-        return static_cast<const HTMLFormControlElement*>(associatedElement);
+        return toHTMLFormControlElement(associatedElement);
     // Assumes the element is an HTMLObjectElement
-    const HTMLElement* element = static_cast<const HTMLObjectElement*>(associatedElement);
-    ASSERT(element->hasTagName(objectTag));
-    return element;
+    return toHTMLObjectElement(associatedElement);
 }
 
 HTMLElement* toHTMLElement(FormAssociatedElement* associatedElement)
 {
     return const_cast<HTMLElement*>(toHTMLElement(static_cast<const FormAssociatedElement*>(associatedElement)));
 }
 
 PassOwnPtr<FormAttributeTargetObserver> FormAttributeTargetObserver::create(const AtomicString& id, FormAssociatedElement* element)
 {
     return adoptPtr(new FormAttributeTargetObserver(id, element));
 }
 
 FormAttributeTargetObserver::FormAttributeTargetObserver(const AtomicString& id, FormAssociatedElement* element)
     : IdTargetObserver(toHTMLElement(element)->treeScope().idTargetObserverRegistry(), id)
     , m_element(element)
 {
 }
 
 void FormAttributeTargetObserver::idTargetChanged()
 {
     m_element->formAttributeTargetChanged();
 }
 
 } // namespace Webcore