Move timer tests to async tests.

tests/isolate/timer_cancel_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_cancel_test;
-
-import 'dart:async';
-import 'dart:isolate';
-import '../../pkg/unittest/lib/unittest.dart';
-
-main() {
-  final ms = const Duration(milliseconds: 1);
-  test("simple timer", () {
-    Timer cancelTimer;
-    int repeatTimer;
-
-    void unreachable() {
-      fail("should not be reached");
-    }
-
-    void handler() {
-      cancelTimer.cancel();
-    }
-
-    void repeatHandler(Timer timer) {
-      repeatTimer++;
-      timer.cancel();
-      expect(repeatTimer, 1);
-    }
-
-    cancelTimer = new Timer(ms * 1000, expectAsync0(unreachable, count: 0));
-    cancelTimer.cancel();
-    new Timer(ms * 1000, expectAsync0(handler));
-    cancelTimer = new Timer(ms * 2000, expectAsync0(unreachable, count: 0));
-    repeatTimer = 0;
-    new Timer.periodic(ms * 1500, expectAsync1(repeatHandler));
-  });
-
-  test("cancel timer with same time", () {
-    var t2;
-    var t1 = new Timer(ms * 0, expectAsync0(() => t2.cancel()));
-    t2 = new Timer(ms * 0, expectAsync0(t1.cancel, count: 0));
-  });
-}