fix analyzer issue in listorder_test

samples/third_party/todomvc/test/listorder_test.dart

Index: samples/third_party/todomvc/test/listorder_test.dart
diff --git a/samples/third_party/todomvc/test/listorder_test.dart b/samples/third_party/todomvc/test/listorder_test.dart
index 99f684462e4a28ea36d0b55e9b8811221597d23b..01d1009f104854f3d32ebcf940d37dc4894541c0 100644
--- a/samples/third_party/todomvc/test/listorder_test.dart
+++ b/samples/third_party/todomvc/test/listorder_test.dart
@@ -6,6 +6,7 @@ library todomvc.test.listorder_test;
 
 import 'dart:html';
 import 'package:polymer/polymer.dart';
+import 'package:polymer/platform.dart' show endOfMicrotask;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import '../web/model.dart';
@@ -19,7 +20,6 @@ import '../web/model.dart';
 _main() {
   useHtmlConfiguration();
 
-
   ShadowRoot root;
 
   setUp(() => Polymer.onReady.then((_) {