Migrated test block 28 to Dart 2.0.

tests/corelib_2/string_source_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.
 
 // Test that different representations of the same string are all equal.
 
 import "dart:convert";
 
 import "package:expect/expect.dart";
 
@@ skipping 15 matching lines @@
     JSON.decode('"\u{10412}"'),
     (JSON.decode('{"\u{10412}":[]}') as Map).keys.first
   ];
   for (String string in strings) {
     Expect.equals(base.length, string.length);
     Expect.equals(base, string);
     Expect.equals(base.hashCode, string.hashCode);
     Expect.listEquals(base.codeUnits.toList(), string.codeUnits.toList());
   }
 }