Introduce isHTMLVideoElement and toHTMLVideoElement

Source/core/html/MediaDocument.cpp

Index: Source/core/html/MediaDocument.cpp
diff --git a/Source/core/html/MediaDocument.cpp b/Source/core/html/MediaDocument.cpp
index aeacbcfec72f6fb0448537c6d18f9004811ddb07..c3a5511e02b0e11faae1565722cebe9dc7efcbf6 100644
--- a/Source/core/html/MediaDocument.cpp
+++ b/Source/core/html/MediaDocument.cpp
@@ -90,7 +90,7 @@ void MediaDocumentParser::createDocumentStructure()
 
     RefPtr<Element> mediaElement = document()->createElement(videoTag, false);
 
-    m_mediaElement = static_cast<HTMLVideoElement*>(mediaElement.get());
+    m_mediaElement = toHTMLVideoElement(mediaElement.get());
     m_mediaElement->setAttribute(controlsAttr, "");
     m_mediaElement->setAttribute(autoplayAttr, "");
 
@@ -133,13 +133,13 @@ static inline HTMLVideoElement* descendentVideoElement(Node* node)
 {
     ASSERT(node);
 
-    if (node->hasTagName(videoTag))
-        return static_cast<HTMLVideoElement*>(node);
+    if (isHTMLVideoElement(node))
+        return toHTMLVideoElement(node);
 
     RefPtr<NodeList> nodeList = node->getElementsByTagNameNS(videoTag.namespaceURI(), videoTag.localName());
-   
+
     if (nodeList.get()->length() > 0)
-        return static_cast<HTMLVideoElement*>(nodeList.get()->item(0));
+        return toHTMLVideoElement(nodeList.get()->item(0));
 
     return 0;
 }