Add const versions of some toHTMLFooElement().

Source/core/html/HTMLObjectElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 101 matching lines @@
     bool m_docNamedItem : 1;
     bool m_useFallbackContent : 1;
 };
 
 inline HTMLObjectElement* toHTMLObjectElement(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(HTMLNames::objectTag));
     return static_cast<HTMLObjectElement*>(node);
 }
 
+inline const HTMLObjectElement* toHTMLObjectElement(const FormAssociatedElement* element)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!element || !element->isFormControlElement());
+    const HTMLObjectElement* objectElement = static_cast<const HTMLObjectElement*>(element);
+    // We need to assert after the cast because FormAssociatedElement doesn't
+    // have hasTagName.
+    ASSERT_WITH_SECURITY_IMPLICATION(!objectElement || objectElement->hasTagName(HTMLNames::objectTag));
+    return objectElement;
+}
+
 }
 
 #endif