Roll Observatory packages and add a roll script

usage/lib/src/uuid.dart

-// Copyright (c) 2014, 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.
-
-/**
- * A UUID generator library.
- */
-library usage.uuid;
-
-import 'dart:math' show Random;
-
-/**
- * A UUID generator. This will generate unique IDs in the format:
- *
- *     f47ac10b-58cc-4372-a567-0e02b2c3d479
- *
- * The generated uuids are 128 bit numbers encoded in a specific string format.
- *
- * For more information, see
- * http://en.wikipedia.org/wiki/Universally_unique_identifier.
- */
-class Uuid {
-  Random _random = new Random();
-
-  /**
-   * Generate a version 4 (random) uuid. This is a uuid scheme that only uses
-   * random numbers as the source of the generated uuid.
-   */
-  String generateV4() {
-    // Generate xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx / 8-4-4-4-12.
-    int special = 8 + _random.nextInt(4);
-
-    return
-        '${_bitsDigits(16, 4)}${_bitsDigits(16, 4)}-'
-        '${_bitsDigits(16, 4)}-'
-        '4${_bitsDigits(12, 3)}-'
-        '${_printDigits(special,  1)}${_bitsDigits(12, 3)}-'
-        '${_bitsDigits(16, 4)}${_bitsDigits(16, 4)}${_bitsDigits(16, 4)}';
-  }
-
-  String _bitsDigits(int bitCount, int digitCount) =>
-      _printDigits(_generateBits(bitCount), digitCount);
-
-  int _generateBits(int bitCount) => _random.nextInt(1 << bitCount);
-
-  String _printDigits(int value, int count) =>
-      value.toRadixString(16).padLeft(count, '0');
-}