Generate dart2js and analyzer files for shared messages.

pkg/dart_messages/bin/json_converter.dart

-// Copyright (c) 2015, 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 'dart:convert';
-import 'dart:io';
-
-import '../lib/shared_messages.dart' as shared_messages;
-
-/// Translates the shared messages in `../lib/shared_messages` to JSON and
-/// emits it into `../lib/shared_messages.json`.
-void main() {
-  var input = shared_messages.MESSAGES;
-  var outPath =
-      Platform.script.resolve('../lib/shared_messages.json').toFilePath();
-  print("Input: ${input.length} entries");
-  print("Output: $outPath");
-  new File(outPath).writeAsStringSync(JSON.encode(shared_messages.MESSAGES));
-  print("Done");
-}