Migrated test block 171 to Dart 2.0.

tests/lib_2/async/schedule_microtask3_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 'dart:async';
+import 'package:async_helper/async_helper.dart';
+import 'package:expect/expect.dart';
+
+main() {
+  // Check that Timers don't run before the async callbacks.
+  bool timerCallbackExecuted = false;
+
+  asyncStart();
+  Timer.run(() {
+    timerCallbackExecuted = true;
+    asyncEnd();
+  });
+
+  scheduleMicrotask(() {
+    Expect.isFalse(timerCallbackExecuted);
+  });
+
+  scheduleMicrotask(() {
+    // Busy loop.
+    var sum = 1;
+    var sw = new Stopwatch()..start();
+    while (sw.elapsedMilliseconds < 5) {
+      sum++;
+    }
+    if (sum == 0) throw "bad"; // Just to use the result.
+    scheduleMicrotask(() {
+      Expect.isFalse(timerCallbackExecuted);
+    });
+  });
+
+  scheduleMicrotask(() {
+    Expect.isFalse(timerCallbackExecuted);
+  });
+}