Use ElementTraversal API in siblingWithAriaRole() to simplify the code

Source/core/accessibility/AXNodeObject.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 353 matching lines @@
     }
     return 0;
 }
 
 static Element* siblingWithAriaRole(String role, Node* node)
 {
     Node* parent = node->parentNode();
     if (!parent)
         return 0;
 
-    for (Node* sibling = parent->firstChild(); sibling; sibling = sibling->nextSibling()) {
-        if (sibling->isElementNode()) {
-            const AtomicString& siblingAriaRole = toElement(sibling)->getAttribute(roleAttr);
-            if (equalIgnoringCase(siblingAriaRole, role))
-                return toElement(sibling);
-        }
+    for (Element* sibling = ElementTraversal::firstChild(*parent); sibling; sibling = ElementTraversal::nextSibling(*sibling)) {
+        const AtomicString& siblingAriaRole = sibling->getAttribute(roleAttr);
+        if (equalIgnoringCase(siblingAriaRole, role))
+            return sibling;
     }
 
     return 0;
 }
 
 Element* AXNodeObject::menuItemElementForMenu() const
 {
     if (ariaRoleAttribute() != MenuRole)
         return 0;
 
@@ skipping 1401 matching lines @@
         useTextUnderElement = true;
 
     if (useTextUnderElement) {
         String text = textUnderElement();
         if (!text.isEmpty())
             textOrder.append(AccessibilityText(text, ChildrenText));
     }
 }
 
 } // namespace WebCore