Migrated test block 171 to Dart 2.0.

tests/lib/async/schedule_microtask2_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 run_async_test;
-
-import 'package:expect/expect.dart';
-import 'dart:async';
-import 'package:unittest/unittest.dart';
-
-main() {
-  // Check that the callbacks are executed in order.
-  test("run async in order test", () {
-    int lastCallback = -1;
-    for (int i = 0; i < 100; i++) {
-      scheduleMicrotask(expectAsync(() {
-        Expect.equals(lastCallback, i - 1);
-        lastCallback = i;
-      }));
-    }
-  });
-}