Roll Observatory packages and add a roll script

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
-/// the file at that path.
-typedef DateTime MockTimeCallback(String path);
-
-MockTimeCallback _mockTimeCallback;
-
-/// Overrides the default behavior for accessing a file's modification time
-/// with [callback].
-///
-/// The OS file modification time has pretty rough granularity (like a few
-/// seconds) which can make for slow tests that rely on modtime. This lets you
-/// replace it with something you control.
-void mockGetModificationTime(MockTimeCallback callback) {
-  _mockTimeCallback = callback;
-}
-
-/// 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);
-}