Make dart2js String.split match the VM version.

tests/corelib/string_split_reg_exp_test.dart

-// Copyright (c) 2012, 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 list = "a b c".split(new RegExp(" "));
-  Expect.equals(3, list.length);
-  Expect.equals("a", list[0]);
-  Expect.equals("b", list[1]);
-  Expect.equals("c", list[2]);
-
-  list = "adbdc".split(new RegExp("[dz]"));
-  Expect.equals(3, list.length);
-  Expect.equals("a", list[0]);
-  Expect.equals("b", list[1]);
-  Expect.equals("c", list[2]);
-
-  list = "addbddc".split(new RegExp("dd"));
-  Expect.equals(3, list.length);
-  Expect.equals("a", list[0]);
-  Expect.equals("b", list[1]);
-  Expect.equals("c", list[2]);
-
-  list = "abc".split(new RegExp(r"b$"));
-  Expect.equals(1, list.length);
-  Expect.equals("abc", list[0]);
-
-  list = "abc".split(new RegExp(""));
-  Expect.equals(3, list.length);
-  Expect.equals("a", list[0]);
-  Expect.equals("b", list[1]);
-  Expect.equals("c", list[2]);
-
-  list = "   ".split(new RegExp("[ ]"));
-  Expect.equals(4, list.length);
-  Expect.equals("", list[0]);
-  Expect.equals("", list[1]);
-  Expect.equals("", list[2]);
-  Expect.equals("", list[3]);
-
-  list = "aaa".split(new RegExp(r"a$"));
-  Expect.equals(2, list.length);
-  Expect.equals("aa", list[0]);
-  Expect.equals("", list[1]);
-}