attempt to deflake IE9 mutation observer test

pkg/custom_element/test/custom_element_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library custom_element.test.custom_element_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:custom_element/custom_element.dart';
 import 'package:unittest/html_config.dart';
@@ skipping 19 matching lines @@
 
     var xtag = null;
     registerCustomElement('fancy-button', () => xtag = new FancyButton());
     expect(xtag, isNotNull, reason: 'FancyButton was created');
     expect(element.xtag, xtag, reason: 'xtag pointer should be set');
     expect(xtag.host, element, reason: 'host pointer should be set');
     expect(xtag.lifecycle, ['created']);
     return new Future(() {
       expect(xtag.lifecycle, ['created', 'inserted']);
       element.remove();
-      return new Future(() {
+      // TODO(jmesserly): the extra future here is to give IE9 time to deliver
+      // its event. This seems wrong. We'll probably need some cooperation
+      // between Dart and the polyfill to coordinate the microtask event loop.
+      return new Future(() => new Future(() {
         expect(xtag.lifecycle, ['created', 'inserted', 'removed']);
-      });
+      }));
     });
   });
 
   test('create a component in code', () {
     var element = createElement('super-button');
     expect(element.xtag, element, reason: 'element not registered');
 
     var xtag = null;
     registerCustomElement('super-button', () => xtag = new FancyButton());
 
@@ skipping 28 matching lines @@
   }
   inserted() {
     super.inserted();
     lifecycle.add('inserted');
   }
   removed() {
     super.removed();
     lifecycle.add('removed');
   }
 }