Roll Observatory packages and add a roll script

packages/watcher/lib/src/file_watcher/polling.dart

 // Copyright (c) 2015, 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 watcher.file_watcher.polling;
 
 import 'dart:async';
 import 'dart:io';
 
 import '../file_watcher.dart';
@@ skipping 73 matching lines @@
       _lastModified = modified;
       _eventsController.add(new WatchEvent(ChangeType.MODIFY, path));
     }
   }
 
   void close() {
     _timer.cancel();
     _eventsController.close();
   }
 }