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

Source/bindings/v8/V8WindowShell.cpp

Index: Source/bindings/v8/V8WindowShell.cpp
diff --git a/Source/bindings/v8/V8WindowShell.cpp b/Source/bindings/v8/V8WindowShell.cpp
index fb0f3dfae23f518514c20d6254c0714cc65f3ef6..f5013a38d5aaebc4a30d2bb42f2323716c532727 100644
--- a/Source/bindings/v8/V8WindowShell.cpp
+++ b/Source/bindings/v8/V8WindowShell.cpp
@@ -425,8 +425,9 @@ static v8::Handle<v8::Value> getNamedProperty(HTMLDocument* htmlDocument, const
 
     if (items->hasExactlyOneItem()) {
         Element* element = items->item(0);
+        ASSERT(element);
         LocalFrame* frame = 0;
-        if (element->hasTagName(HTMLNames::iframeTag) && (frame = toHTMLIFrameElement(element)->contentFrame()))
+        if (isHTMLIFrameElement(*element) && (frame = toHTMLIFrameElement(*element).contentFrame()))
             return toV8(frame->domWindow(), creationContext, isolate);
         return toV8(element, creationContext, isolate);
     }