Bug 940754 - Fix rooting hazard in WorkerPrivateParent::WrapObject() r=bent

dom/workers/WorkerPrivate.cpp

@@ -2159,7 +2159,8 @@ WorkerPrivateParent<Derived>::WrapObject(JSContext* aCx,
 
   AssertIsOnParentThread();
 
-  JSObject* obj = WorkerBinding::Wrap(aCx, aScope, ParentAsWorkerPrivate());
+  JS::Rooted<JSObject*> obj(aCx, WorkerBinding::Wrap(aCx, aScope,
+                                                     ParentAsWorkerPrivate()));
 
   if (mRooted) {
     PreserveWrapper(this);