Remove usage of dart:json.

pkg/intl/test/message_extraction/make_hardcoded_translation.dart

 #!/usr/bin/env 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.
 
 /**
  * This simulates a translation process, reading the messages generated
  * from extract_message.dart for the files sample_with_messages.dart and
  * part_of_sample_with_messages.dart and writing out hard-coded translations for
  * German and French locales.
  */
 
+import 'dart:convert';
 import 'dart:io';
-import 'dart:json' as json;
 import 'package:path/path.dart' as path;
 import 'package:args/args.dart';
 import 'package:intl/src/intl_message.dart';
 import 'package:serialization/serialization.dart';
 
 /**
  * A serialization so that we can write out the more complex plural and
  * gender examples to JSON easily. This is a stopgap and should be replaced
  * with a commonly used translation file format.
  */
@@ skipping 188 matching lines @@
  * Generate a translated json version from [originals] in [locale] looking
  * up the translations in [translations].
  */
 void translate(List originals, String locale, Map translations) {
   var translated = {"_locale" : locale};
   for (var each in originals) {
     var name = each["name"];
     translated[name] = translations[name];
   }
   var file = new File(path.join(targetDir, 'translation_$locale.json'));
-  file.writeAsStringSync(json.stringify(translated));
+  file.writeAsStringSync(JSON.encode(translated));
 }
 
 main() {
   var args = new Options().arguments;
   if (args.length == 0) {
     print('Usage: generate_hardcoded_translation [--output-dir=<dir>] '
         '[originalFile.json]');
     exit(0);
   }
   var parser = new ArgParser();
   parser.addOption("output-dir", defaultsTo: '.',
       callback: (value) => targetDir = value);
   parser.parse(args);
 
   var fileArgs = args.where((x) => x.contains('.json'));
 
-  var messages = json.parse(new File(fileArgs.first).readAsStringSync());
+  var messages = JSON.decode(new File(fileArgs.first).readAsStringSync());
   translate(messages, "fr", french);
   translate(messages, "de_DE", german);
 }