Port ParentNode API to ElementTraversal

Source/core/dom/ContainerNode.cpp

Index: Source/core/dom/ContainerNode.cpp
diff --git a/Source/core/dom/ContainerNode.cpp b/Source/core/dom/ContainerNode.cpp
index 4350dcea063e1d1e673f664675c290279a88525a..d63b98e908235bd54bd1ea1d68fd517d04e89bab 100644
--- a/Source/core/dom/ContainerNode.cpp
+++ b/Source/core/dom/ContainerNode.cpp
@@ -880,30 +880,6 @@ PassRefPtr<HTMLCollection> ContainerNode::children()
     return ensureRareData().ensureNodeLists().addCache<HTMLCollection>(this, NodeChildren);
 }
 
-Element* ContainerNode::firstElementChild() const
-{
-    return ElementTraversal::firstWithin(*this);
-}
-
-Element* ContainerNode::lastElementChild() const
-{
-    Node* n = lastChild();
-    while (n && !n->isElementNode())
-        n = n->previousSibling();
-    return toElement(n);
-}
-
-unsigned ContainerNode::childElementCount() const
-{
-    unsigned count = 0;
-    Node* n = firstChild();
-    while (n) {
-        count += n->isElementNode();
-        n = n->nextSibling();
-    }
-    return count;
-}
-
 unsigned ContainerNode::childNodeCount() const
 {
     unsigned count = 0;