Add iterator object to iterate efficiently over an Element's attributes

Source/core/xml/XPathStep.cpp

Index: Source/core/xml/XPathStep.cpp
diff --git a/Source/core/xml/XPathStep.cpp b/Source/core/xml/XPathStep.cpp
index bf490bab10b51c75580ffcfcabfaf721046bf013..a6ec7764749e1dda19ea1117df1f35f6edb98d64 100644
--- a/Source/core/xml/XPathStep.cpp
+++ b/Source/core/xml/XPathStep.cpp
@@ -357,9 +357,10 @@ void Step::nodesInAxis(Node* context, NodeSet& nodes) const
             if (!contextElement->hasAttributes())
                 return;
 
-            unsigned attributeCount = contextElement->attributeCount();
-            for (unsigned i = 0; i < attributeCount; ++i) {
-                RefPtrWillBeRawPtr<Attr> attr = contextElement->ensureAttr(contextElement->attributeItem(i).name());
+            AttributeIteratorAccessor attributes = contextElement->attributesIterator();
+            AttributeConstIterator end = attributes.end();
+            for (AttributeConstIterator it = attributes.begin(); it != end; ++it) {
+                RefPtrWillBeRawPtr<Attr> attr = contextElement->ensureAttr(it->name());
                 if (nodeMatches(attr.get(), AttributeAxis, nodeTest()))
                     nodes.append(attr.release());
             }