Use new is*Element() helper functions more in rendering code

Source/core/rendering/compositing/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 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 303 matching lines @@
 
 static RenderVideo* findFullscreenVideoRenderer(Document& document)
 {
     Element* fullscreenElement = FullscreenElementStack::fullscreenElementFrom(document);
     while (fullscreenElement && fullscreenElement->isFrameOwnerElement()) {
         Document* contentDocument = toHTMLFrameOwnerElement(fullscreenElement)->contentDocument();
         if (!contentDocument)
             return 0;
         fullscreenElement = FullscreenElementStack::fullscreenElementFrom(*contentDocument);
     }
-    if (!fullscreenElement || !fullscreenElement->hasTagName(videoTag))
+    if (!isHTMLVideoElement(fullscreenElement))
         return 0;
     RenderObject* renderer = fullscreenElement->renderer();
     if (!renderer)
         return 0;
     return toRenderVideo(renderer);
 }
 
 void RenderLayerCompositor::finishCompositingUpdateForFrameTree(LocalFrame* frame)
 {
     for (LocalFrame* child = frame->tree().firstChild(); child; child = child->tree().nextSibling())
@@ skipping 1908 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "LocalFrame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore