Introduce the NotificationEvent object.

Source/modules/notifications/NotificationEvent.idl

Index: Source/modules/notifications/NotificationEvent.idl
diff --git a/Source/modules/notifications/NotificationEvent.idl b/Source/modules/notifications/NotificationEvent.idl
new file mode 100644
index 0000000000000000000000000000000000000000..b089670e6e811fdb6fbba7a0eee7c132989691e7
--- /dev/null
+++ b/Source/modules/notifications/NotificationEvent.idl
@@ -0,0 +1,14 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://notifications.spec.whatwg.org/#service-worker-api
+
+// FIXME: NotificationEvent should support being constructed from JavaScript.
+[
+    Exposed=ServiceWorker,
+    RuntimeEnabled=ServiceWorkerNotifications,
+    TypeChecking=Interface,
+] interface NotificationEvent : ExtendableEvent {
+    readonly attribute Notification notification;
+};