Roll Observatory packages and add a roll script

packages/observe/lib/src/change_notifier.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.change_notifier;
 
 import 'dart:async';
 import 'dart:collection' show UnmodifiableListView;
 import 'package:observe/observe.dart';
 import 'package:observe/src/observable.dart' show notifyPropertyChangeHelper;
@@ skipping 61 matching lines @@
   void notifyChange(ChangeRecord record) {
     if (!hasObservers) return;
 
     if (_records == null) {
       _records = [];
       scheduleMicrotask(deliverChanges);
     }
     _records.add(record);
   }
 }