Bug 742422. Make DOM prototypes more typeinference-friendly. r=peterv

dom/bindings/Utils.cpp

@@ -69,7 +69,8 @@ CreateInterfacePrototypeObject(JSContext* cx, JSObject* global,
                                JSPropertySpec* properties,
                                ConstantSpec* constants)
 {
-  JSObject* ourProto = JS_NewObject(cx, protoClass, parentProto, global);
+  JSObject* ourProto = JS_NewObjectWithUniqueType(cx, protoClass, parentProto,
+                                                  global);
   if (!ourProto) {
     return NULL;
   }