Migrate async tests to strong

tests/lib_strong/async/stream_periodic3_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.
+
+// Test merging streams.
+library dart.test.stream_from_iterable;
+
+import "dart:async";
+import 'package:unittest/unittest.dart';
+
+// The stopwatch is more precise than the Timer.
+// Some browsers (Firefox and IE so far) can trigger too early. So we add more
+// 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) ? 5 : 0;
+
+main() {
+  test("stream-periodic3", () {
+    Stopwatch watch = new Stopwatch()..start();
+    Stream stream = new Stream.periodic(const Duration(milliseconds: 1),
+                                        (x) => x);
+    stream.take(10).listen((_) { }, onDone: expectAsync(() {
+      int millis = watch.elapsedMilliseconds + safetyMargin;
+      expect(millis, greaterThanOrEqualTo(10));
+    }));
+  });
+}