Port ParentNode API to ElementTraversal

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 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef ParentNode_h
 #define ParentNode_h
 
 #include "core/dom/ContainerNode.h"
+#include "core/dom/ElementTraversal.h"
 
 namespace WebCore {
 
 class ParentNode {
 public:
     static PassRefPtr<HTMLCollection> children(ContainerNode* node)
     {
         return node->children();
     }
 
     static Element* firstElementChild(ContainerNode* node)
     {
-        return node->firstElementChild();
+        ASSERT(node);
+        return ElementTraversal::firstWithin(*node);
     }
 
     static Element* lastElementChild(ContainerNode* node)
     {
-        return node->lastElementChild();
+        ASSERT(node);
+        return ElementTraversal::lastWithin(*node);
     }
 
     static unsigned childElementCount(ContainerNode* node)
     {
-        return node->childElementCount();
+        ASSERT(node);
+        unsigned count = 0;
+        for (Element* child = ElementTraversal::firstWithin(*node); child; child = ElementTraversal::nextSibling(*child))
+            ++count;
+        return count;
     }
 };
 
 } // namespace WebCore
 
 #endif // ParentNode_h