Have HTMLCollection::item() return an Element as per specification

Source/core/dom/LiveNodeList.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 58 matching lines @@
     }
 
     virtual ~LiveNodeListBase()
     {
         if (type() != ChildNodeListType)
             document().unregisterNodeList(this);
     }
 
     ContainerNode& rootNode() const;
     bool overridesItemAfter() const { return m_overridesItemAfter; }
-    Node* itemBefore(const Node* previousItem) const;
 
     ALWAYS_INLINE bool hasIdNameCache() const { return !isLiveNodeListType(type()); }
     ALWAYS_INLINE bool isRootedAtDocument() const { return m_rootType == NodeListIsRootedAtDocument || m_rootType == NodeListIsRootedAtDocumentIfOwnerHasItemrefAttr; }
     ALWAYS_INLINE NodeListInvalidationType invalidationType() const { return static_cast<NodeListInvalidationType>(m_invalidationType); }
     ALWAYS_INLINE CollectionType type() const { return static_cast<CollectionType>(m_collectionType); }
     ContainerNode* ownerNode() const { return m_ownerNode.get(); }
     ALWAYS_INLINE void invalidateCache(const QualifiedName* attrName) const
     {
         if (!attrName || shouldInvalidateTypeOnAttributeChange(invalidationType(), *attrName))
             invalidateCache();
         else if (hasIdNameCache() && (*attrName == HTMLNames::idAttr || *attrName == HTMLNames::nameAttr))
             invalidateIdNameCacheMaps();
     }
     virtual void invalidateCache() const = 0;
 
     static bool shouldInvalidateTypeOnAttributeChange(NodeListInvalidationType, const QualifiedName&);
 
 protected:
     Document& document() const { return m_ownerNode->document(); }
 
     ALWAYS_INLINE NodeListRootType rootType() const { return static_cast<NodeListRootType>(m_rootType); }
     bool shouldOnlyIncludeDirectChildren() const { return m_shouldOnlyIncludeDirectChildren; }
 
+    template <typename Collection>
+    static Element* iterateForPreviousNode(const Collection&, Node* current);
+    template <typename Collection>
+    static Element* itemBefore(const Collection&, const Node* previousItem);
+
 private:
-    Node* iterateForPreviousNode(Node* current) const;
     void invalidateIdNameCacheMaps() const;
 
     RefPtr<ContainerNode> m_ownerNode; // Cannot be null.
     const unsigned m_rootType : 2;
     const unsigned m_invalidationType : 4;
     const unsigned m_shouldOnlyIncludeDirectChildren : 1;
     const unsigned m_collectionType : 5;
 
     // From HTMLCollection
     const unsigned m_overridesItemAfter : 1;
@@ skipping 34 matching lines @@
     virtual unsigned length() const OVERRIDE FINAL { return m_collectionIndexCache.nodeCount(*this); }
     virtual Node* item(unsigned offset) const OVERRIDE FINAL { return m_collectionIndexCache.nodeAt(*this, offset); }
     virtual Node* namedItem(const AtomicString&) const OVERRIDE FINAL;
     virtual bool nodeMatches(const Element&) const = 0;
     // Avoid ambiguity since both NodeList and LiveNodeListBase have an ownerNode() method.
     using LiveNodeListBase::ownerNode;
 
     virtual void invalidateCache() const OVERRIDE FINAL;
 
     // Collection IndexCache API.
+    Node* itemBefore(const Node* previousItem) const;
     Node* traverseToFirstElement(const ContainerNode& root) const;
     Node* traverseForwardToOffset(unsigned offset, Node& currentNode, unsigned& currentOffset, const ContainerNode& root) const;
 
 private:
     virtual bool isLiveNodeList() const OVERRIDE FINAL { return true; }
 
-    mutable CollectionIndexCache<LiveNodeList> m_collectionIndexCache;
+    mutable CollectionIndexCache<LiveNodeList, Node> m_collectionIndexCache;
 };
 
 } // namespace WebCore
 
 #endif // LiveNodeList_h