Use DEFINE_NODE_TYPE_CASTS instead of using manual toHTMLFooElement()

Source/core/html/HTMLTrackElement.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:
  * 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 78 matching lines @@
     virtual void textTrackAddCue(TextTrack*, PassRefPtr<TextTrackCue>);
     virtual void textTrackRemoveCue(TextTrack*, PassRefPtr<TextTrackCue>);
 
     LoadableTextTrack* ensureTrack();
     virtual bool canLoadUrl(const KURL&);
 
     RefPtr<LoadableTextTrack> m_track;
     Timer<HTMLTrackElement> m_loadTimer;
 };
 
-inline HTMLTrackElement* toHTMLTrackElement(Node* node)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(HTMLNames::trackTag));
-    return static_cast<HTMLTrackElement*>(node);
-}
+DEFINE_NODE_TYPE_CASTS(HTMLTrackElement, hasTagName(HTMLNames::trackTag));
 
 }
 
 #endif