Make required dictionary members non-nullable again

third_party/WebKit/LayoutTests/http/tests/notifications/resources/serviceworker-notification-event.js

 importScripts('../../serviceworker/resources/worker-testharness.js');
 
 let messagePort = null;
 addEventListener('message', workerEvent => {
     messagePort = workerEvent.data;
     messagePort.postMessage('ready');
 });
 
 addEventListener('notificationclick', e => runTest(e.notification));
 
 // Test body for the serviceworker-notification-event.html layout test.
 function runTest(notification) {
     assert_true('NotificationEvent' in self);
 
     assert_throws(null, () => new NotificationEvent('NotificationEvent'));
     assert_throws(null, () => new NotificationEvent('NotificationEvent', {}));
+    assert_throws(null, () => new NotificationEvent('NotificationEvent', { notification: null }));
 
     const event = new NotificationEvent('NotificationEvent', { notification });
 
     assert_equals(event.type, 'NotificationEvent');
     assert_idl_attribute(event, 'notification');
     assert_idl_attribute(event, 'action');
     assert_equals(event.cancelable, false);
     assert_equals(event.bubbles, false);
     assert_equals(event.notification, notification);
     assert_equals(event.action, '');
     assert_inherits(event, 'waitUntil');
 
     const customEvent = new NotificationEvent('NotificationEvent', {
                             notification: notification,
                             bubbles: true,
                             cancelable: true });
 
     assert_equals(customEvent.type, 'NotificationEvent');
     assert_equals(customEvent.cancelable, true);
     assert_equals(customEvent.bubbles, true);
     assert_equals(customEvent.notification, notification);
 
     // Signal to the document that the test has finished running.
     messagePort.postMessage(true /* success */);
 }