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

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 22dc2f6d7cd12b32c150bd522c46cd3dbfff24d7..b7b902418b7b853ceee71a46db26e24b6db0425a 100644
--- a/Source/core/html/MediaDocument.cpp
+++ b/Source/core/html/MediaDocument.cpp
@@ -29,7 +29,7 @@
 
 #include "HTMLNames.h"
 #include "bindings/v8/ExceptionStatePlaceholder.h"
-#include "core/dom/NodeTraversal.h"
+#include "core/dom/ElementTraversal.h"
 #include "core/dom/RawDataDocumentParser.h"
 #include "core/events/KeyboardEvent.h"
 #include "core/events/ThreadLocalEventNames.h"
@@ -129,18 +129,6 @@ PassRefPtr<DocumentParser> MediaDocument::createParser()
     return MediaDocumentParser::create(this);
 }
 
-static inline HTMLVideoElement* descendentVideoElement(Node* root)
-{
-    ASSERT(root);
-
-    for (Node* node = root; node; node = NodeTraversal::next(*node, root)) {
-        if (node->hasTagName(videoTag))
-            return toHTMLVideoElement(node);
-    }
-
-    return 0;
-}
-
 void MediaDocument::defaultEventHandler(Event* event)
 {
     Node* targetNode = event->target()->toNode();
@@ -148,7 +136,7 @@ void MediaDocument::defaultEventHandler(Event* event)
         return;
 
     if (event->type() == EventTypeNames::keydown && event->isKeyboardEvent()) {
-        HTMLVideoElement* video = descendentVideoElement(targetNode);
+        HTMLVideoElement* video = Traversal<HTMLVideoElement>::firstWithin(*targetNode);
         if (!video)
             return;