Replace string uses with code units in Json parser.

tools/testing/dart/test_options.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.
 
 library test_options_parser;
 
 import "dart:io";
 import "drt_updater.dart";
 import "test_suite.dart";
 import "utils.dart";
 import "compiler_configuration.dart" show CompilerConfiguration;
 import "runtime_configuration.dart" show RuntimeConfiguration;
 
 const List<String> defaultTestSelectors =
-    const ['language', 'corelib', 'unsorted', 'coroutine', 'ffi', 'io'];
+    const ['language', 'corelib', 'unsorted', 'coroutine', 'ffi', 'io',
+           'samples'];
 
 /**
  * Specification of a single test option.
  *
  * The name of the specification is used as the key for the option in
  * the Map returned from the [TestOptionParser] parse method.
  */
 class _TestOptionSpecification {
   _TestOptionSpecification(this.name,
                            this.description,
@@ skipping 869 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }