Bug 1283674 P0 Drop cached controlling ServiceWorker ref when ServiceWorkerContainer window is disconnect. r=baku

dom/workers/ServiceWorkerContainer.cpp

@@ -69,6 +69,7 @@ ServiceWorkerContainer::~ServiceWorkerContainer()
 void
 ServiceWorkerContainer::DisconnectFromOwner()
 {
+  mControllerWorker = nullptr;
   RemoveReadyPromise();
   DOMEventTargetHelper::DisconnectFromOwner();
 }