Use stricter typing for HTMLCollection named getter

Source/core/html/HTMLFrameSetElement.cpp

Index: Source/core/html/HTMLFrameSetElement.cpp
diff --git a/Source/core/html/HTMLFrameSetElement.cpp b/Source/core/html/HTMLFrameSetElement.cpp
index db0043491203ad814be74cfdcc3f181dc0b8f96a..2d8bb5dd45d24169d06d6916149e221244aa111c 100644
--- a/Source/core/html/HTMLFrameSetElement.cpp
+++ b/Source/core/html/HTMLFrameSetElement.cpp
@@ -219,10 +219,10 @@ void HTMLFrameSetElement::willRecalcStyle(StyleRecalcChange)
 
 DOMWindow* HTMLFrameSetElement::anonymousNamedGetter(const AtomicString& name)
 {
-    Node* frameNode = children()->namedItem(name);
-    if (!frameNode || !frameNode->hasTagName(HTMLNames::frameTag))
+    Element* frameElement = children()->namedItem(name);
+    if (!frameElement || !frameElement->hasTagName(HTMLNames::frameTag))
         return 0;
-    Document* document = toHTMLFrameElement(frameNode)->contentDocument();
+    Document* document = toHTMLFrameElement(frameElement)->contentDocument();
     if (!document || !document->frame())
         return 0;
     return document->domWindow();