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

Source/core/html/HTMLSummaryElement.cpp

 /*
  * Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 43 matching lines @@
 
 void HTMLSummaryElement::didAddUserAgentShadowRoot(ShadowRoot& root)
 {
     root.appendChild(DetailsMarkerControl::create(document()));
     root.appendChild(HTMLContentElement::create(document()));
 }
 
 HTMLDetailsElement* HTMLSummaryElement::detailsElement() const
 {
     Node* parent = NodeRenderingTraversal::parent(this);
-    if (parent && parent->hasTagName(detailsTag))
+    if (isHTMLDetailsElement(parent))
         return toHTMLDetailsElement(parent);
     return 0;
 }
 
 bool HTMLSummaryElement::isMainSummary() const
 {
     if (HTMLDetailsElement* details = detailsElement())
         return details->findMainSummary() == this;
 
     return false;
@@ skipping 57 matching lines @@
 
 bool HTMLSummaryElement::willRespondToMouseClickEvents()
 {
     if (isMainSummary() && renderer())
         return true;
 
     return HTMLElement::willRespondToMouseClickEvents();
 }
 
 }