Migrate async tests to strong

tests/lib_strong/async/timer_cancel2_test.dart

+// Copyright (c) 2012, 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 timer_cancel2_test;
+
+import 'dart:async';
+import 'package:unittest/unittest.dart';
+
+main() {
+  // Test that a timeout handler can cancel itself.
+  test("timer cancel test 2", () {
+    var cancelTimer;
+
+    void cancelHandler(Timer timer) {
+      cancelTimer.cancel();
+    }
+
+    cancelTimer = new Timer.periodic(const Duration(milliseconds: 1),
+                                     expectAsync(cancelHandler));
+  });
+}