Migrated test block 23 to Dart 2.0.

tests/corelib_2/regexp/range-bound-ffff_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
@@ skipping 15 matching lines @@
 import 'package:expect/expect.dart';
 
 void main() {
   description(
       'Test for rdar:/68455379, a case-insensitive regex containing a character class containing a range with an upper bound of \uFFFF can lead to an infinite-loop.');
 
   shouldBe(
       firstMatch("A", new RegExp(r"[\u0001-\uFFFF]", caseSensitive: false)),
       ["A"]);
 }