Make HTMLCollection / NodeList backward traversal consistent with forward one

Source/core/dom/ChildNodeList.cpp

Index: Source/core/dom/ChildNodeList.cpp
diff --git a/Source/core/dom/ChildNodeList.cpp b/Source/core/dom/ChildNodeList.cpp
index d87dec6e81c0538a3cf5bb8832274c9f4bb3c633..8c72856e08ece51e5ed21997f0bc876decc3895b 100644
--- a/Source/core/dom/ChildNodeList.cpp
+++ b/Source/core/dom/ChildNodeList.cpp
@@ -44,11 +44,6 @@ ChildNodeList::~ChildNodeList()
     m_parent->nodeLists()->removeChildNodeList(this);
 }
 
-Node* ChildNodeList::itemBefore(const Node* previous) const
-{
-    return LIKELY(!!previous) ? previous->previousSibling() : rootNode().lastChild();
-}
-
 Node* ChildNodeList::traverseForwardToOffset(unsigned offset, Node& currentNode, unsigned& currentOffset) const
 {
     ASSERT(currentOffset < offset);
@@ -60,4 +55,15 @@ Node* ChildNodeList::traverseForwardToOffset(unsigned offset, Node& currentNode,
     return 0;
 }
 
+Node* ChildNodeList::traverseBackwardToOffset(unsigned offset, Node& currentNode, unsigned& currentOffset) const
+{
+    ASSERT(currentOffset > offset);
+    Node* previous = &currentNode;
+    while ((previous = previous->previousSibling())) {
+        if (--currentOffset == offset)
+            return previous;
+    }
+    return 0;
+}
+
 } // namespace WebCore