Introduce isHTMLVideoElement and toHTMLVideoElement

Source/core/html/shadow/MediaControlElements.cpp

 /*
  * Copyright (C) 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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.
@@ skipping 677 matching lines @@
     }
 
     HTMLMediaElement* mediaElement = toParentMediaElement(this);
     // 1. If the media element is an audio element, or is another playback
     // mechanism with no rendering area, abort these steps. There is nothing to
     // render.
     if (!mediaElement || !mediaElement->isVideo())
         return;
 
     // 2. Let video be the media element or other playback mechanism.
-    HTMLVideoElement* video = static_cast<HTMLVideoElement*>(mediaElement);
+    HTMLVideoElement* video = toHTMLVideoElement(mediaElement);
 
     // 3. Let output be an empty list of absolutely positioned CSS block boxes.
     Vector<RefPtr<HTMLDivElement> > output;
 
     // 4. If the user agent is exposing a user interface for video, add to
     // output one or more completely transparent positioned CSS block boxes that
     // cover the same region as the user interface.
 
     // 5. If the last time these rules were run, the user agent was not exposing
     // a user interface for video, but now it is, let reset be true. Otherwise,
@@ skipping 95 matching lines @@
     CueList activeCues = mediaElement->currentlyActiveCues();
     for (size_t i = 0; i < activeCues.size(); ++i) {
         TextTrackCue* cue = activeCues[i].data();
         cue->videoSizeDidChange(m_videoDisplaySize.size());
     }
 }
 
 // ----------------------------
 
 } // namespace WebCore