Introduce isHTMLVideoElement and toHTMLVideoElement

Source/core/html/HTMLVideoElement.h

 /*
  * Copyright (C) 2007, 2008, 2009, 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 75 matching lines @@
     virtual bool hasAvailableVideoFrame() const;
     virtual void updateDisplayState();
     virtual void didMoveToNewDocument(Document* oldDocument) OVERRIDE;
     virtual void setDisplayMode(DisplayMode);
 
     OwnPtr<HTMLImageLoader> m_imageLoader;
 
     AtomicString m_defaultPosterURL;
 };
 
+inline bool isHTMLVideoElement(const Node* node)
+{
+    return node->hasTagName(HTMLNames::videoTag);
+}
+
+inline bool isHTMLVideoElement(const Element* element)
+{
+    return element->hasTagName(HTMLNames::videoTag);
+}
+
+inline HTMLVideoElement* toHTMLVideoElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || isHTMLVideoElement(node));
+    return static_cast<HTMLVideoElement*>(node);
+}
+
 } //namespace
 
 #endif