Bug 1383128 - Avoid some useless AddRef()s when parsing class attributes; r=smaug

dom/base/nsAttrValue.cpp

@@ -1303,7 +1303,7 @@ nsAttrValue::ParseAtomArray(const nsAString& aValue)
 
   AtomArray* array = GetAtomArrayValue();
 
-  if (!array->AppendElement(classAtom)) {
+  if (!array->AppendElement(Move(classAtom))) {
     Reset();
     return;
   }
@@ -1318,7 +1318,7 @@ nsAttrValue::ParseAtomArray(const nsAString& aValue)
 
     classAtom = NS_AtomizeMainThread(Substring(start, iter));
 
-    if (!array->AppendElement(classAtom)) {
+    if (!array->AppendElement(Move(classAtom))) {
       Reset();
       return;
     }