Migrated test block 19 to Dart 2.0.

tests/corelib_strong/reg_exp_start_end_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";
-
-main() {
-  var matches = new RegExp("(a(b)((c|de)+))").allMatches("abcde abcde abcde");
-  var it = matches.iterator;
-  int start = 0;
-  int end = 5;
-  while (it.moveNext()) {
-    Match match = it.current;
-    Expect.equals(start, match.start);
-    Expect.equals(end, match.end);
-    start += 6;
-    end += 6;
-  }
-}