Migrate async tests to strong

tests/lib_strong/async/catch_errors18_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.
+
+import 'package:async_helper/async_helper.dart';
+import "package:expect/expect.dart";
+import 'dart:async';
+import 'catch_errors.dart';
+
+main() {
+  asyncStart();
+  Completer done = new Completer();
+
+  var events = [];
+  Stream stream = new Stream.periodic(const Duration(milliseconds: 20),
+                                      (x) => x);
+  // Test that errors of periodic streams are caught.
+  catchErrors(() {
+    var subscription;
+    subscription = stream.listen((x) {
+      if (x == 5) {
+        events.add("cancel");
+        subscription.cancel();
+        done.complete(true);
+        return;
+      }
+      events.add(x);
+    });
+  }).listen((x) { events.add("outer: $x"); },
+            onDone: () { Expect.fail("Unexpected callback"); });
+
+  done.future.whenComplete(() {
+    // Give handlers time to run.
+    Timer.run(() {
+      Expect.listEquals([0, 1, 2, 3, 4, "cancel"], events);
+      asyncEnd();
+    });
+  });
+}