Make timer test more robust.

tests/lib/async/timer_regress22626_test.dart

 // Copyright (c) 2015, 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.
 
 // Test that no wakeups are being dropped if we cancel timers.
 // WARNING: For this test to work it cannot rely on any other async features
 // and will just timeout if it is failing.
 
 library timer_regress22626_test;
 
 import 'dart:async';
 import 'dart:math';
 import 'package:expect/expect.dart';
 
-int countdown = 10;
+int countdown = 5;
 var rng = new Random(1234);
 
 void test(int delay, int delta) {
   var t0 = new Timer(new Duration(milliseconds: delay + delta),
                      () => Expect.fail("should have been cancelled by now"));
   new Timer(Duration.ZERO, () => t0.cancel());
   new Timer(Duration.ZERO,
             () => new Timer(new Duration(milliseconds: delay),
                             () {
                               if (--countdown == 0) {
                                 print("done");
                               } else {
                                 test(delay, max(0, delta + rng.nextInt(2) - 1));
                               }
                             }));
 }
 
 void main() {
-  test(50, 2);
+  test(200, 2);
 }