Migrated test block 20 to Dart 2.0.

tests/corelib_2/regexp/many-brackets_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 24 matching lines @@
   for (var i = 0; i < count; ++i) regexp += "(";
   regexp += "hello";
   for (var i = 0; i < count; ++i) regexp += ")";
 
   var manyHellosArray = [];
   for (var i = 0; i <= count; ++i) manyHellosArray.add("hello");
 
   var manyBracketsRegExp = new RegExp(regexp);
   shouldBe(firstMatch('hello', manyBracketsRegExp), manyHellosArray);
 }