Allow non-primitive-value dictionaries to be passed to constructors for html

tests/html/notifications_test.dart

 library NotificationsTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlIndividualConfiguration();
 
   group('supported', () {
     test('supported', () {
@@ skipping 10 matching lines @@
 
   group('webkitNotifications', () {
     if (NotificationCenter.supported) {
       test('DomException', () {
         try {
           window.notifications.createNotification('', '', '');
         } on DomException catch (e) {
           expect(e.name, DomException.SECURITY);
         }
       });
+
+      test('construct notification', () {
+        var note = new Notification('this is a notification');
+        var note2 = new Notification('another notificiation',
+          {'option1': 'foo'});
+      });
     }
   });
 }