Add toHTMLFieldSetElement and toHTMLLegendElement, and use them.

Source/core/accessibility/AccessibilityNodeObject.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 882 matching lines @@
 
     return toElement(node)->innerText();
 }
 
 AccessibilityObject* AccessibilityNodeObject::titleUIElement() const
 {
     if (!node() || !node()->isElementNode())
         return 0;
 
     if (isFieldset())
-        return axObjectCache()->getOrCreate(static_cast<HTMLFieldSetElement*>(node())->legend());
+        return axObjectCache()->getOrCreate(toHTMLFieldSetElement(node())->legend());
 
     HTMLLabelElement* label = labelForElement(toElement(node()));
     if (label)
         return axObjectCache()->getOrCreate(label);
 
     return 0;
 }
 
 AccessibilityButtonState AccessibilityNodeObject::checkboxOrRadioValue() const
 {
@@ skipping 885 matching lines @@
         useTextUnderElement = true;
 
     if (useTextUnderElement) {
         String text = textUnderElement();
         if (!text.isEmpty())
             textOrder.append(AccessibilityText(text, ChildrenText));
     }
 }
 
 } // namespace WebCore