Roll Observatory packages and add a roll script

packages/quiver/lib/testing/src/async/async.dart

 // Copyright 2013 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 30 matching lines @@
     this.callback = callback;
     return this;
   }
 
   void cancel() {
     if (onCancel != null) onCancel();
   }
 
   bool isActive = true;
 }