Migrate async tests to strong

tests/lib_strong/async/catch_errors6_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();
+  var completer = new Completer();
+  var errorHandlerOrDoneHasBeenExecuted = false;
+  // Test that `catchErrors` doesn't shut down if a future is never completed.
+  catchErrors(() {
+    completer.future.then((x) { Expect.fail("should not be executed"); });
+  }).listen((x) {
+      errorHandlerOrDoneHasBeenExecuted = true;
+      Expect.fail("should not be executed (listen)");
+    },
+    onDone: () {
+      errorHandlerOrDoneHasBeenExecuted = true;
+      Expect.fail("should not be executed (onDone)");
+    });
+  Timer.run(() {
+    Expect.isFalse(errorHandlerOrDoneHasBeenExecuted);
+    asyncEnd();
+  });
+}