Migrate async tests to strong

tests/lib_strong/async/future_delayed_error_test.dart

+// Copyright (c) 2012, 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.
+
+library future_delayed_error_test;
+
+import 'package:async_helper/async_helper.dart';
+import "package:expect/expect.dart";
+import 'dart:async';
+
+testImmediateError() {
+  asyncStart();
+  var future = new Future.error("error");
+  future.catchError((error) {
+    Expect.equals(error, "error");
+    asyncEnd();
+  });
+}
+
+Future get completedFuture {
+  var completer = new Completer();
+  completer.completeError("foobar");
+  return completer.future;
+}
+
+testDelayedError() {
+  asyncStart();
+  completedFuture.catchError((error) {
+    Expect.equals(error, "foobar");
+    asyncEnd();
+  });
+}
+
+main() {
+  testImmediateError();
+  testDelayedError();
+}
+