Bug 1336529 Handle ServiceWorkerInfo destruction while released KeepAliveToken. r=asuth

dom/workers/ServiceWorkerManager.cpp

@@ -1374,7 +1374,7 @@ void
 ServiceWorkerManager::WorkerIsIdle(ServiceWorkerInfo* aWorker)
 {
   AssertIsOnMainThread();
-  MOZ_ASSERT(aWorker);
+  MOZ_DIAGNOSTIC_ASSERT(aWorker);
 
   RefPtr<ServiceWorkerRegistrationInfo> reg =
     GetRegistration(aWorker->GetPrincipal(), aWorker->Scope());

dom/workers/ServiceWorkerPrivate.cpp

@@ -2072,7 +2072,11 @@ ServiceWorkerPrivate::ReleaseToken()
   --mTokenCount;
   if (!mTokenCount) {
     TerminateWorker();
-  } else if (IsIdle()) {
+  }
+
+  // mInfo can be nullptr here if NoteDeadServiceWorkerInfo() is called while
+  // the KeepAliveToken is being proxy released as a runnable.
+  else if (mInfo && IsIdle()) {
     RefPtr<ServiceWorkerManager> swm = ServiceWorkerManager::GetInstance();
     if (swm) {
       swm->WorkerIsIdle(mInfo);