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

Source/core/html/HTMLDialogElement.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 27 matching lines @@
 namespace WebCore {
 
 using namespace HTMLNames;
 
 // This function chooses the focused element when showModal() is invoked, as described in the spec for showModal().
 static void setFocusForModalDialog(HTMLDialogElement* dialog)
 {
     Element* focusableDescendant = 0;
     Node* next = 0;
     for (Node* node = dialog->firstChild(); node; node = next) {
-        if (node->hasTagName(dialogTag))
+        if (isHTMLDialogElement(*node))
             next = NodeTraversal::nextSkippingChildren(*node, dialog);
         else
             next = NodeTraversal::next(*node, dialog);
 
         if (!node->isElementNode())
             continue;
         Element* element = toElement(node);
         if (element->isFormControlElement()) {
             HTMLFormControlElement* control = toHTMLFormControlElement(node);
             if (control->isAutofocusable()) {
@@ skipping 140 matching lines @@
 {
     if (event->type() == EventTypeNames::cancel) {
         closeDialog();
         event->setDefaultHandled();
         return;
     }
     HTMLElement::defaultEventHandler(event);
 }
 
 } // namespace WebCore