Add const versions of some toHTMLFooElement().

Source/core/html/HTMLFrameOwnerElement.h

 /*
  * Copyright (C) 2006, 2007, 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 65 matching lines @@
     Frame* m_contentFrame;
     SandboxFlags m_sandboxFlags;
 };
 
 inline HTMLFrameOwnerElement* toHTMLFrameOwnerElement(Node* node)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!node || node->isFrameOwnerElement());
     return static_cast<HTMLFrameOwnerElement*>(node);
 }
 
+inline const HTMLFrameOwnerElement* toHTMLFrameOwnerElement(const Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->isFrameOwnerElement());
+    return static_cast<const HTMLFrameOwnerElement*>(node);
+}
+
 class SubframeLoadingDisabler {
 public:
     explicit SubframeLoadingDisabler(Node* root)
         : m_root(root)
     {
         disabledSubtreeRoots().add(m_root);
     }
 
     ~SubframeLoadingDisabler()
     {
@@ skipping 15 matching lines @@
         DEFINE_STATIC_LOCAL(HashCountedSet<Node*>, nodes, ());
         return nodes;
     }
 
     Node* m_root;
 };
 
 } // namespace WebCore
 
 #endif // HTMLFrameOwnerElement_h