Have ElementData::attributeItem() return a reference

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 97e32ebc62dbb31aee63d8a687e94b2cd75c1560..8be6e8a1722c1264be70af5c7f672e29f3ff3306 100644
--- a/Source/core/editing/MarkupAccumulator.cpp
+++ b/Source/core/editing/MarkupAccumulator.cpp
@@ -381,7 +381,7 @@ void MarkupAccumulator::appendElement(StringBuilder& result, Element& element, N
     if (element.hasAttributes()) {
         unsigned length = element.attributeCount();
         for (unsigned int i = 0; i < length; i++)
-            appendAttribute(result, element, *element.attributeItem(i), namespaces);
+            appendAttribute(result, element, element.attributeItem(i), namespaces);
     }
 
     // Give an opportunity to subclasses to add their own attributes.