Add dart_messages package.

pkg/dart_messages/bin/message_id.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:math' as math;
+
+import '../lib/shared_messages.dart' as shared_messages;
+
+math.Random random = new math.Random();
+
+const idLength = 6;
+final $A = "A".codeUnitAt(0);
+final $Z = "Z".codeUnitAt(0);
+
+String computeId() {
+  List charCodes = [];
+  for (int i = 0; i < idLength; i++) {
+    charCodes.add($A + random.nextInt($Z - $A));
+  }
+  return new String.fromCharCodes(charCodes);
+}
+
+/// Computes a random message ID that hasn't been used before.
+void main() {
+  var usedIds =
+      shared_messages.MESSAGES.values.map((entry) => entry['id']).toSet();
+
+  print("${usedIds.length} existing ids");
+
+  var newId;
+  do {
+    newId = computeId();
+  } while (!usedIds.contains(newId));
+  print("Available id: $newId");
+}