Roll Observatory packages and add a roll script

packages/observe/lib/src/path_observer.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.path_observer;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' show min;
 
@@ skipping 909 matching lines @@
       if (observer._isOpen) observer._iterateObjects(observe);
     }
 
     for (var observer in _observers.toList(growable: false)) {
       if (observer._isOpen) observer._check();
     }
   }
 }
 
 const int _MAX_DIRTY_CHECK_CYCLES = 1000;