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

Source/core/editing/MarkupAccumulator.cpp

Index: Source/core/editing/MarkupAccumulator.cpp
diff --git a/Source/core/editing/MarkupAccumulator.cpp b/Source/core/editing/MarkupAccumulator.cpp
index b0d91fd56c46757010032988f38c3304faa2716b..2942db3b428e3c3fb98735b771e6d6230424da05 100644
--- a/Source/core/editing/MarkupAccumulator.cpp
+++ b/Source/core/editing/MarkupAccumulator.cpp
@@ -385,9 +385,10 @@ void MarkupAccumulator::appendElement(StringBuilder& result, Element& element, N
     appendOpenTag(result, element, namespaces);
 
     if (element.hasAttributes()) {
-        unsigned length = element.attributeCount();
-        for (unsigned i = 0; i < length; i++)
-            appendAttribute(result, element, element.attributeItem(i), namespaces);
+        AttributeIteratorAccessor attributes = element.attributesIterator();
+        AttributeConstIterator end = attributes.end();
+        for (AttributeConstIterator it = attributes.begin(); it != end; ++it)
+            appendAttribute(result, element, **it, namespaces);
     }
 
     // Give an opportunity to subclasses to add their own attributes.