Have NodeList::item() overrides return an Element* when appropriate

Source/core/dom/LiveNodeList.h

Index: Source/core/dom/LiveNodeList.h
diff --git a/Source/core/dom/LiveNodeList.h b/Source/core/dom/LiveNodeList.h
index 46e03a3150802a805e597a1afa824840aec6334f..ca2da3aedd1a4082c2bfd204d07462ac0c70c20f 100644
--- a/Source/core/dom/LiveNodeList.h
+++ b/Source/core/dom/LiveNodeList.h
@@ -42,7 +42,7 @@ public:
         : LiveNodeListBase(ownerNode, rootType, invalidationType, collectionType) { }
 
     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 Element* item(unsigned offset) const OVERRIDE FINAL { return m_collectionIndexCache.nodeAt(*this, offset); }
     virtual bool elementMatches(const Element&) const = 0;
 
     virtual void invalidateCache(Document* oldDocument = 0) const OVERRIDE FINAL;