Migrated test block 19 to Dart 2.0.

tests/corelib_2/reg_exp_groups_test.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "package:expect/expect.dart";
 
 // Dart test program for RegExp.groups.
 
 class RegExpGroupsTest {
   static testMain() {
     var match = new RegExp("(a(b)((c|de)+))").firstMatch("abcde");
     var groups = match.groups([0, 4, 2, 3]);
     Expect.equals('abcde', groups[0]);
     Expect.equals('de', groups[1]);
     Expect.equals('b', groups[2]);
     Expect.equals('cde', groups[3]);
   }
 }
 
 main() {
   RegExpGroupsTest.testMain();
 }