Roll Observatory packages and add a roll script

packages/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;
 }