Roll Observatory packages and add a roll script

dart_style/lib/src/fast_hash.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.
-
-library dart_style.src.fast_hash;
-
-/// A mixin for classes with identity equality that need to be frequently
-/// hashed.
-abstract class FastHash {
-  static int _nextId = 0;
-
-  /// A semi-unique numeric indentifier for the object.
-  ///
-  /// This is useful for debugging and also speeds up using the object in hash
-  /// sets. Ids are *semi*-unique because they may wrap around in long running
-  /// processes. Since objects are equal based on their identity, this is
-  /// innocuous and prevents ids from growing without bound.
-  final int id = _nextId = (_nextId + 1) & 0x0fffffff;
-
-  int get hashCode => id;
-}