Migrated test block 171 to Dart 2.0.

tests/lib_2/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:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
-import 'package:async_helper/async_helper.dart';
 import 'dart:async';
 
 main() {
-  StackTrace trace;
-  asyncStart();
-  var f = new Future(() {
-    throw "foo";
-  });
-  f.catchError((e, st) {
-    Expect.equals("foo", e);
-    Expect.isNotNull(st);
-    asyncEnd();
-  });
+  int lastCallback = -1;
+  for (int i = 0; i < 100; i++) {
+    asyncStart();
+    scheduleMicrotask(() {
+      Expect.equals(lastCallback, i - 1);
+      lastCallback = i;
+      asyncEnd();
+    });
+  }
 }