Have ElementData::attributeItem() return a reference

Source/web/WebElement.cpp

Index: Source/web/WebElement.cpp
diff --git a/Source/web/WebElement.cpp b/Source/web/WebElement.cpp
index 1fac295b3eadad7cf3a5516c2f668103163fb15f..2130461b8a37572ded80a06cccb6f38d7d24e5e5 100644
--- a/Source/web/WebElement.cpp
+++ b/Source/web/WebElement.cpp
@@ -125,14 +125,14 @@ WebString WebElement::attributeLocalName(unsigned index) const
 {
     if (index >= attributeCount())
         return WebString();
-    return constUnwrap<Element>()->attributeItem(index)->localName();
+    return constUnwrap<Element>()->attributeItem(index).localName();
 }
 
 WebString WebElement::attributeValue(unsigned index) const
 {
     if (index >= attributeCount())
         return WebString();
-    return constUnwrap<Element>()->attributeItem(index)->value();
+    return constUnwrap<Element>()->attributeItem(index).value();
 }
 
 WebString WebElement::innerText()