Migrate async tests to strong

tests/lib_strong/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;
+      }));
+    }
+  });
+}