Migrate async tests to strong

tests/lib_strong/async/stream_periodic4_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';
+
+void runTest(period, maxElapsed, pauseDuration) {
+  Function done = expectAsync(() { });
+
+  Stopwatch watch = new Stopwatch()..start();
+  Stream stream = new Stream.periodic(period, (x) => x);
+  var subscription;
+  subscription = stream.take(5).listen((i) {
+    if (watch.elapsed > maxElapsed) {
+      // Test failed in this configuration. Try with more time (or give up
+      // if we reached an unreasonable maxElapsed).
+      if (maxElapsed > const Duration(seconds: 2)) {
+        // Give up.
+        expect(true, false);
+      } else {
+        subscription.cancel();
+        // Call 'done' ourself, since it won't be invoked in the onDone handler.
+        runTest(period * 2, maxElapsed * 2, pauseDuration * 2);
+        done();
+        return;
+      }
+    }
+    watch.reset();
+    if (i == 2) {
+      subscription.pause();
+      watch.stop();
+      new Timer(pauseDuration, () {
+        watch.start();
+        subscription.resume();
+      });
+    }
+  }, onDone: done);
+}
+
+main() {
+  test("stream-periodic4", () {
+    runTest(const Duration(milliseconds: 2),
+            const Duration(milliseconds: 8),
+            const Duration(milliseconds: 10));
+  });
+}