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

Source/core/html/HTMLFieldSetElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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
@@ skipping 89 matching lines @@
 void HTMLFieldSetElement::refreshElementsIfNeeded() const
 {
     uint64_t docVersion = document().domTreeVersion();
     if (m_documentVersion == docVersion)
         return;
 
     m_documentVersion = docVersion;
 
     m_associatedElements.clear();
 
-    for (Element* element = ElementTraversal::firstWithin(*this); element; element = ElementTraversal::next(*element, this)) {
-        if (element->hasTagName(objectTag)) {
+    for (HTMLElement* element = Traversal<HTMLElement>::firstWithin(*this); element; element = Traversal<HTMLElement>::next(*element, this)) {
+        if (isHTMLObjectElement(*element)) {
             m_associatedElements.append(toHTMLObjectElement(element));
             continue;
         }
 
         if (!element->isFormControlElement())
             continue;
 
         m_associatedElements.append(toHTMLFormControlElement(element));
     }
 }
 
 const Vector<FormAssociatedElement*>& HTMLFieldSetElement::associatedElements() const
 {
     refreshElementsIfNeeded();
     return m_associatedElements;
 }
 
 } // namespace