Migrate async tests to strong

tests/lib_strong/async/catch_errors3_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();
+  bool futureWasExecuted = false;
+  bool future2WasExecuted = false;
+
+  // Make sure `catchErrors` never closes its stream.
+  catchErrors(() {
+    new Future(() => 499).then((x) {
+      futureWasExecuted = true;
+    });
+    scheduleMicrotask(() {
+      new Future(() => 42).then((x) {
+        future2WasExecuted = true;
+        Expect.isTrue(futureWasExecuted);
+        done.complete(true);
+      });
+    });
+    return 'allDone';
+  }).listen((x) {
+      Expect.fail("Unexpected callback");
+    },
+    onDone: () {
+      Expect.fail("Unexpected callback");
+    });
+  done.future.whenComplete(asyncEnd);
+}