Make sure the rootNode of a LiveNodeListBase is always a ContainerNode

Source/core/dom/LiveNodeList.cpp

Index: Source/core/dom/LiveNodeList.cpp
diff --git a/Source/core/dom/LiveNodeList.cpp b/Source/core/dom/LiveNodeList.cpp
index 8f3bd6e8fe3a0ac00f0541add1d0b282416eaddc..56c164ad1b0e15b4b404e876cfb111d669807d64 100644
--- a/Source/core/dom/LiveNodeList.cpp
+++ b/Source/core/dom/LiveNodeList.cpp
@@ -28,21 +28,13 @@
 
 namespace WebCore {
 
-Node& LiveNodeListBase::rootNode() const
+ContainerNode& LiveNodeListBase::rootNode() const
 {
     if (isRootedAtDocument() && m_ownerNode->inDocument())
         return m_ownerNode->document();
     return *m_ownerNode;
 }
 
-ContainerNode* LiveNodeListBase::rootContainerNode() const
-{
-    Node& rootNode = this->rootNode();
-    if (!rootNode.isContainerNode())
-        return 0;
-    return toContainerNode(&rootNode);
-}
-
 void LiveNodeListBase::invalidateCache() const
 {
     m_cachedItem = 0;