Roll Observatory packages and add a roll script

packages/watcher/lib/src/stat.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.stat;
 
 import 'dart:async';
 import 'dart:io';
 
 /// A function that takes a file path and returns the last modified time for
@@ skipping 13 matching lines @@
 }
 
 /// Gets the modification time for the file at [path].
 Future<DateTime> getModificationTime(String path) {
   if (_mockTimeCallback != null) {
     return new Future.value(_mockTimeCallback(path));
   }
 
   return FileStat.stat(path).then((stat) => stat.modified);
 }