Bug 1304566 - Unregister from the obsever service in order to prevent re-entrancy; r=janv

dom/quota/ActorsParent.cpp

@@ -2813,6 +2813,18 @@ ShutdownObserver::Observe(nsISupports* aSubject,
   MOZ_ASSERT(!strcmp(aTopic, PROFILE_BEFORE_CHANGE_QM_OBSERVER_ID));
   MOZ_ASSERT(gInstance);
 
+  nsCOMPtr<nsIObserverService> observerService =
+    mozilla::services::GetObserverService();
+  if (NS_WARN_IF(!observerService)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Unregister ourselves from the observer service first to make sure the
+  // nested event loop below will not cause re-entrancy issues.
+  Unused <<
+    observerService->RemoveObserver(this,
+                                    PROFILE_BEFORE_CHANGE_QM_OBSERVER_ID);
+
   QuotaManagerService* qms = QuotaManagerService::Get();
   MOZ_ASSERT(qms);