Migrate async tests to strong

tests/lib_strong/async/catch_errors2_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();
+  bool futureWasExecuted = false;
+  Future done;
+
+  // Error streams never close.
+  catchErrors(() {
+    done = new Future(() {
+      futureWasExecuted = true;
+    });
+    return 'allDone';
+  }).listen((x) {
+      Expect.fail("Unexpected callback");
+    },
+    onDone: () {
+      Expect.fail("Unexpected callback");
+    });
+
+  done.whenComplete(asyncEnd);
+}