Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/watcher/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';
+
+import 'package:stack_trace/stack_trace.dart';
+
+/// 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 Chain.track(FileStat.stat(path)).then((stat) => stat.modified);
+}