Migrated test block 25 to Dart 2.0.

tests/corelib/safe_to_string_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() {
-  Expect.stringEquals('1', Error.safeToString(1));
-  Expect.stringEquals('0.5', Error.safeToString(0.5));
-  Expect.stringEquals('"1"', Error.safeToString("1"));
-  Expect.stringEquals('"\'"', Error.safeToString("'"));
-  Expect.stringEquals('"\'\'"', Error.safeToString("''"));
-  Expect.stringEquals(r'"\""', Error.safeToString('"'));
-  Expect.stringEquals(r'"\"\""', Error.safeToString('""'));
-
-  Expect.stringEquals(r'"\\\"\n\r"', Error.safeToString('\\"\n\r'));
-
-  Expect.stringEquals(r'"\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007"',
-      Error.safeToString('\x00\x01\x02\x03\x04\x05\x06\x07'));
-  Expect.stringEquals(r'"\b\t\n\u000b\f\r\u000e\u000f"',
-      Error.safeToString('\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f'));
-  Expect.stringEquals(r'"\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017"',
-      Error.safeToString('\x10\x11\x12\x13\x14\x15\x16\x17'));
-  Expect.stringEquals(r'"\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f"',
-      Error.safeToString('\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f'));
-  Expect.stringEquals('" "', Error.safeToString(" "));
-
-  Expect.stringEquals('null', Error.safeToString(null));
-  Expect.stringEquals('true', Error.safeToString(true));
-  Expect.stringEquals('false', Error.safeToString(false));
-  // The class name may be minified.
-  String className = "$Object";
-  Expect.stringEquals(
-      "Instance of '$className'", Error.safeToString(new Object()));
-}