Migrated test block 23 to Dart 2.0.

tests/corelib_2/regexp/regexp_kde_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 98 matching lines @@
 
   str = "abcDdcba";
   // The returned array contains D, d.
   re = new RegExp(r"d", caseSensitive: false);
   var matches = re.allMatches(str);
   Expect.listEquals(matches.map((m) => m.group(0)).toList(), ['D', 'd']);
 
   // unicode escape sequence
   shouldBe(firstMatch('abc', new RegExp(r"\u0062")), ['b']);
 }