Disallow constructing the Notification object in a Service Worker.

LayoutTests/http/tests/notifications/resources/serviceworker-notification-constructor.js

+importScripts('../../serviceworker/resources/worker-testharness.js');
+importScripts('../../resources/testharness-helpers.js');
+
+test(function() {
+    assert_true('Notification' in self);
+
+    assert_throws({ name: 'TypeError' }, function() {
+        new Notification();
+    });
+
+}, 'Constructing a Notification object in a Service Worker throws.');