[flow] Add types for ServiceWorker show notification api

Summary:
I'm trying to improve the types used in our service worker infra and this is a missing type not defined anywhere.

So adding it here.

Spec:

https://notifications.spec.whatwg.org/#service-worker-api

Changelog: [libdef] Add libdef types for `getNotifications` and `showNotification` API for `ServiceWorkerRegistration`

Reviewed By: SamChou19815

Differential Revision: D66535415

fbshipit-source-id: b83b3514218230c9b7bc21744c352fd70f99a6f4

lib/serviceworkers.js

@@ -132,6 +132,11 @@ declare class PushManager {
 
 type ServiceWorkerUpdateViaCache = 'imports' | 'all' | 'none';
 
+type GetNotificationOptions = {
+  tag?: string,
+  ...
+};
+
 declare class ServiceWorkerRegistration extends EventTarget {
   +installing: ?ServiceWorker,
   +waiting: ?ServiceWorker,
@@ -141,6 +146,8 @@ declare class ServiceWorkerRegistration extends EventTarget {
   +updateViaCache: ServiceWorkerUpdateViaCache,
   +pushManager: PushManager,
 
+  getNotifications?: (filter?: GetNotificationOptions) => Promise<$ReadOnlyArray<Notification>>,
+  showNotification?: (title: string, options?: NotificationOptions) => Promise<void>,
   update(): Promise<void>,
   unregister(): Promise<boolean>,