Have HTMLCollection::item() return an Element as per specification

Source/web/WebPageSerializerImpl.cpp

Index: Source/web/WebPageSerializerImpl.cpp
diff --git a/Source/web/WebPageSerializerImpl.cpp b/Source/web/WebPageSerializerImpl.cpp
index 4eed2f03b7f7f8646c70b5a22c6370b4b4d6ffad..a2b7705831973b07453dac353a514cc0ede8cf3b 100644
--- a/Source/web/WebPageSerializerImpl.cpp
+++ b/Source/web/WebPageSerializerImpl.cpp
@@ -477,10 +477,9 @@ void WebPageSerializerImpl::collectTargetFrames()
         // Go through sub-frames.
         RefPtr<HTMLCollection> all = currentDoc->all();
 
-        for (unsigned i = 0; Node* node = all->item(i); i++) {
-            if (!node->isHTMLElement())
+        for (unsigned i = 0; Element* element = all->item(i); i++) {
+            if (!element->isHTMLElement())
                 continue;
-            Element* element = toElement(node);
             WebFrameImpl* webFrame =
                 WebFrameImpl::fromFrameOwnerElement(element);
             if (webFrame)