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

Source/core/html/FormAssociatedElement.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, 2007 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 90 matching lines @@
 {
     const AtomicString& formId(element->fastGetAttribute(formAttr));
     // 3. If the element is reassociateable, has a form content attribute, and
     // is itself in a Document, then run these substeps:
     if (!formId.isNull() && element->inDocument()) {
         // 3.1. If the first element in the Document to have an ID that is
         // case-sensitively equal to the element's form content attribute's
         // value is a form element, then associate the form-associated element
         // with that form element.
         // 3.2. Abort the "reset the form owner" steps.
-        HTMLFormElement* newForm = 0;
         Element* newFormCandidate = element->treeScope().getElementById(formId);
-        if (newFormCandidate && newFormCandidate->hasTagName(formTag))
-            newForm = toHTMLFormElement(newFormCandidate);
-        return newForm;
+        return isHTMLFormElement(newFormCandidate) ? toHTMLFormElement(newFormCandidate) : 0;
     }
     // 4. Otherwise, if the form-associated element in question has an ancestor
     // form element, then associate the form-associated element with the nearest
     // such ancestor form element.
     return element->findFormAncestor();
 }
 
 void FormAssociatedElement::formRemovedFromTree(const Node& formRoot)
 {
     ASSERT(m_form);
@@ skipping 190 matching lines @@
     , m_element(element)
 {
 }
 
 void FormAttributeTargetObserver::idTargetChanged()
 {
     m_element->formAttributeTargetChanged();
 }
 
 } // namespace Webcore