Clean up toHTMLFooElement() using DEFINE_NODE_TYPE_CASTS_WITH_FUNCTION

Source/core/html/shadow/HTMLContentElement.h

 /*
  * Copyright (C) 2011 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 83 matching lines @@
 inline bool isHTMLContentElement(const Node* node)
 {
     return node->hasTagName(HTMLNames::contentTag);
 }
 
 inline bool isHTMLContentElement(const Element* element)
 {
     return element->hasTagName(HTMLNames::contentTag);
 }
 
-inline HTMLContentElement* toHTMLContentElement(Node* node)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!node || isHTMLContentElement(node));
-    return static_cast<HTMLContentElement*>(node);
-}
+DEFINE_NODE_TYPE_CASTS(HTMLContentElement, hasTagName(HTMLNames::contentTag));
 
 }
 
 #endif