Migrated test block 20 to Dart 2.0.

tests/corelib_2/regexp/negative-special-characters_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 75 matching lines @@
   test("[^\\Sр]", " Проверка ", 8);
   test("[^р\\s]", " Проверка ", 4);
   test("[^\\sр]", " Проверка ", 4);
 
   test("[ф \\s\\S]", "Проверка \\r\\n", 0);
   test("[\\S\\sф ]", "Проверка \\r\\n", 0);
 
   test("[^z]", "Проверка \\r\\n", 0);
   test("[^ф]", "Проверка \\r\\n", 0);
 }