Bug 1230164 P2 Only activate service workers in the activating state. r=ehsan

dom/workers/ServiceWorkerManager.cpp

@@ -2652,7 +2652,8 @@ ServiceWorkerManager::HandleError(JSContext* aCx,
 void
 ServiceWorkerRegistrationInfo::FinishActivate(bool aSuccess)
 {
-  if (mPendingUninstall || !mActiveWorker) {
+  if (mPendingUninstall || !mActiveWorker ||
+      mActiveWorker->State() != ServiceWorkerState::Activating) {
     return;
   }