Roll Observatory packages and add a roll script

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

 // Copyright 2014 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 262 matching lines @@
 
   _FakeTimer._(Duration duration, this._callback, this._isPeriodic, this._time)
       : _duration = duration < _minDuration ? _minDuration : duration {
     _nextCall = _time._elapsed + _duration;
   }
 
   bool get isActive => _time._hasTimer(this);
 
   cancel() => _time._cancelTimer(this);
 }