Migrated test block 20 to Dart 2.0.

tests/corelib_strong/regexp/look-ahead_test.dart

-// Copyright (c) 2014, the Dart project authors. All rights reserved.
-// Copyright 2013 the V8 project authors. All rights reserved.
-// Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions
-// are met:
-// 1.  Redistributions of source code must retain the above copyright
-//     notice, this list of conditions and the following disclaimer.
-// 2.  Redistributions in binary form must reproduce the above copyright
-//     notice, this list of conditions and the following disclaimer in the
-//     documentation and/or other materials provided with the distribution.
-//
-// THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
-// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-// DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
-// DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
-// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
-// ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-import 'v8_regexp_utils.dart';
-import 'package:expect/expect.dart';
-
-void main() {
-  description(
-      'Test for regression against <a href="https://bugs.webkit.org/show_bug.cgi?id=41458">Yarr Interpreter is crashing in some cases of look-ahead regex patterns</a>');
-
-  shouldBe(firstMatch("ab", new RegExp(r"a(?=b|c)")), ["a"]);
-  shouldBe(firstMatch("abd", new RegExp(r"a(?=c|b)|d")), ["a"]);
-}