Move caching out of LiveNodeListBase and into a new CollectionIndexCache class

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 56c164ad1b0e15b4b404e876cfb111d669807d64..c0c2034974f2727ac70a59a019facc92941e6fbc 100644
--- a/Source/core/dom/LiveNodeList.cpp
+++ b/Source/core/dom/LiveNodeList.cpp
@@ -35,18 +35,17 @@ ContainerNode& LiveNodeListBase::rootNode() const
     return *m_ownerNode;
 }
 
-void LiveNodeListBase::invalidateCache() const
-{
-    m_cachedItem = 0;
-    m_isLengthCacheValid = false;
-}
-
 void LiveNodeListBase::invalidateIdNameCacheMaps() const
 {
     ASSERT(hasIdNameCache());
     static_cast<const HTMLCollection*>(this)->invalidateIdNameCacheMaps();
 }
 
+void LiveNodeList::invalidateCache() const
+{
+    m_collectionIndexCache.invalidate();
+}
+
 Node* LiveNodeList::namedItem(const AtomicString& elementId) const
 {
     Node& rootNode = this->rootNode();