Remove usage of dart:json.

pkg/intl/test/message_extraction/extract_to_json.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 script uses the extract_messages.dart library to find the Intl.message
  * calls in the target dart files and produces intl_messages.json containing the
  * information on those messages. It uses the analyzer-experimental parser
  * to find the information.
  *
  * This is intended to test the basic functioning of extracting messages and
  * serve as an example for how a program to extract them to a translation
  * file format could work. In the tests, this file is then run through a
  * simulated translation and the results of that are used to generate code. See
  * message_extraction_test.dart
  *
  * If the environment variable INTL_MESSAGE_OUTPUT is set then it will use
  * that as the output directory, otherwise it will use the working directory.
  */
 library extract_to_json;
 
+import 'dart:convert';
 import 'dart:io';
 import 'package:intl/extract_messages.dart';
-import 'dart:json' as json;
 import 'package:path/path.dart' as path;
 import 'package:intl/src/intl_message.dart';
 import 'package:args/args.dart';
 
 main() {
   var args = new Options().arguments;
   var targetDir;
   var parser = new ArgParser();
   parser.addFlag("suppress-warnings", defaultsTo: false,
       callback: (x) => suppressWarnings = x);
   parser.addFlag("warnings-are-errors", defaultsTo: false,
       callback: (x) => warningsAreErrors = x);
 
   parser.addOption("output-dir", defaultsTo: '.',
       callback: (value) => targetDir = value);
   parser.parse(args);
   if (args.length == 0) {
     print('Usage: extract_to_json [--output-dir=<dir>] [files.dart]');
     print('Accepts Dart files and produces intl_messages.json');
     exit(0);
   }
   var allMessages = [];
   for (var arg in args.where((x) => x.contains(".dart"))) {
     var messages = parseFile(new File(arg));
     messages.forEach((k, v) => allMessages.add(toJson(v)));
   }
   var file = new File(path.join(targetDir, 'intl_messages.json'));
-  file.writeAsStringSync(json.stringify(allMessages));
+  file.writeAsStringSync(JSON.encode(allMessages));
   if (hasWarnings && warningsAreErrors) {
     exit(1);
   }
 }
 
 /**
  * This is a placeholder for transforming a parameter substitution from
  * the translation file format into a Dart interpolation. In our case we
  * store it to the file in Dart interpolation syntax, so the transformation
  * is trivial.
  */
 String leaveTheInterpolationsInDartForm(MainMessage msg, chunk) {
   if (chunk is String) return chunk;
   if (chunk is int) return "\$${msg.arguments[chunk]}";
   return chunk.toCode();
 }
 
 /**
  * Convert the [MainMessage] to a trivial JSON format.
  */
 Map toJson(MainMessage message) {
   var result = new Map<String, Object>();
   for (var attribute in message.attributeNames) {
     result[attribute] = message[attribute];
   }
   result["message"] = message.expanded(leaveTheInterpolationsInDartForm);
   return result;
 }