Use DEFINE_NODE_TYPE_CASTS instead of using manual toHTMLFooElement()

Source/core/html/HTMLSourceElement.h

 /*
  * Copyright (C) 2007, 2008, 2010 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 39 matching lines @@
 
     virtual InsertionNotificationRequest insertedInto(ContainerNode*) OVERRIDE;
     virtual void removedFrom(ContainerNode*) OVERRIDE;
     virtual bool isURLAttribute(const Attribute&) const OVERRIDE;
 
     void errorEventTimerFired(Timer<HTMLSourceElement>*);
 
     Timer<HTMLSourceElement> m_errorEventTimer;
 };
 
-inline HTMLSourceElement* toHTMLSourceElement(Node* node)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(HTMLNames::sourceTag));
-    return static_cast<HTMLSourceElement*>(node);
-}
+DEFINE_NODE_TYPE_CASTS(HTMLSourceElement, hasTagName(HTMLNames::sourceTag));
 
 } // namespace WebCore
 
 #endif