Migrate async tests to strong

tests/lib_strong/async/timer_repeat_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_repeat_test;
+
+import 'dart:async';
+import 'package:unittest/unittest.dart';
+
+const Duration TIMEOUT = const Duration(milliseconds: 500);
+const int ITERATIONS = 5;
+
+Timer timer;
+Stopwatch stopwatch = new Stopwatch();
+int iteration;
+
+// Some browsers (Firefox and IE so far) can trigger too early. Add a safety
+// margin. We use identical(1, 1.0) as an easy way to know if the test is
+// compiled by dart2js.
+int get safetyMargin => identical(1, 1.0) ? 100 : 0;
+
+void timeoutHandler(Timer timer) {
+  iteration++;
+  expect(iteration, lessThanOrEqualTo(ITERATIONS));
+  if (iteration == ITERATIONS) {
+    // When we are done with all of the iterations, we expect a
+    // certain amount of time to have passed.  Checking the time on
+    // each iteration doesn't work because the timeoutHandler runs
+    // concurrently with the periodic timer.
+    expect(stopwatch.elapsedMilliseconds + safetyMargin,
+           greaterThanOrEqualTo(ITERATIONS * TIMEOUT.inMilliseconds));
+    timer.cancel();
+  }
+}
+
+main() {
+  test("timer_repeat", () {
+    iteration = 0;
+    stopwatch.start();
+    timer = new Timer.periodic(TIMEOUT,
+        expectAsync(timeoutHandler, count: ITERATIONS));
+  });
+}