Make HTMLCollection / NodeList backward traversal consistent with forward one

Source/core/dom/ParentNode.h

 /*
  * Copyright (C) 2013 Samsung Electronics. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 27 matching lines @@
 
 class ParentNode {
 public:
     static PassRefPtr<HTMLCollection> children(ContainerNode& node)
     {
         return node.children();
     }
 
     static Element* firstElementChild(ContainerNode& node)
     {
-        return ElementTraversal::firstWithin(node);
+        return ElementTraversal::firstChild(node);
     }
 
     static Element* lastElementChild(ContainerNode& node)
     {
-        return ElementTraversal::lastWithin(node);
+        return ElementTraversal::lastChild(node);
     }
 
     static unsigned childElementCount(ContainerNode& node)
     {
         unsigned count = 0;
         for (Element* child = ElementTraversal::firstWithin(node); child; child = ElementTraversal::nextSibling(*child))
             ++count;
         return count;
     }
 };
 
 } // namespace WebCore
 
 #endif // ParentNode_h