Migrated test block 171 to Dart 2.0.

tests/lib_strong/async/run_zoned7_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.
-
-import 'package:async_helper/async_helper.dart';
-import "package:expect/expect.dart";
-import 'dart:async';
-import 'catch_errors.dart';
-
-main() {
-  asyncStart();
-  Completer done = new Completer();
-
-  var events = [];
-  // Test runZoned with periodic Timers.
-  runZoned(() {
-    int counter = 0;
-    new Timer.periodic(const Duration(milliseconds: 50), (timer) {
-      if (counter == 5) {
-        timer.cancel();
-        done.complete(true);
-      }
-      counter++;
-      events.add(counter);
-    });
-  });
-
-  done.future.whenComplete(() {
-    Expect.listEquals([
-      "main exit",
-      1,
-      2,
-      3,
-      4,
-      5,
-      6,
-    ], events);
-    asyncEnd();
-  });
-  events.add("main exit");
-}