Migrated test block 15 to Dart 2.0.

tests/corelib/list_to_string2_test.dart

-// Copyright (c) 2013, 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() {
-  List list = [1, 2];
-  list.add(list);
-
-  List list2 = new List(4);
-  list2[0] = 1;
-  list2[1] = 2;
-  list2[2] = list2;
-  list2[3] = list;
-
-  Expect.equals("[1, 2, [...]]", list.toString());
-  Expect.equals("[1, 2, [...], [1, 2, [...]]]", list2.toString());
-
-  // Throwing in the middle of a toString does not leave the
-  // list as being visited.
-  List list3 = [1, 2, new ThrowOnToString(), 4];
-  Expect.throws(list3.toString, (e) => e == "Bad!");
-  list3[2] = 3;
-  Expect.equals("[1, 2, 3, 4]", list3.toString());
-}
-
-class ThrowOnToString {
-  String toString() {
-    throw "Bad!";
-  }
-}