Roll Observatory packages and add a roll script

packages/watcher/lib/src/directory_watcher/mac_os.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 watcher.directory_watcher.mac_os;
 
 import 'dart:async';
 import 'dart:io';
 
 import '../directory_watcher.dart';
@@ skipping 379 matching lines @@
     if (!isReady) return;
     _eventsController.add(new WatchEvent(type, path));
   }
 
   /// Emit an error, then close the watcher.
   void _emitError(error, StackTrace stackTrace) {
     _eventsController.addError(error, stackTrace);
     close();
   }
 }