Migrated test block 171 to Dart 2.0.

tests/lib/async/stack_trace05_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:expect/expect.dart';
-import 'package:async_helper/async_helper.dart';
-import 'dart:async';
-
-StackTrace captureStackTrace() {
-  try {
-    throw 0;
-  } catch (e, st) {
-    return st;
-  }
-}
-
-main() {
-  StackTrace trace = captureStackTrace();
-  asyncStart();
-  var f = new Future(() => 499);
-  f.then((_) => new Future.error("e", trace)).whenComplete(() => 499).then((_) {
-    throw "should never be reached";
-  }).catchError((e, st) {
-    Expect.equals("e", e);
-    Expect.identical(trace, st);
-    asyncEnd();
-  });
-}