Roll Observatory packages and add a roll script

packages/observe/lib/src/observable.dart

 // Copyright (c) 2013, 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 observe.src.observable;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:smoke/smoke.dart' as smoke;
@@ skipping 149 matching lines @@
 // public instead?
 // NOTE: this is not exported publically.
 notifyPropertyChangeHelper(Observable obj, Symbol field, Object oldValue,
     Object newValue) {
 
   if (obj.hasObservers && oldValue != newValue) {
     obj.notifyChange(new PropertyChangeRecord(obj, field, oldValue, newValue));
   }
   return newValue;
 }