Wrap Directory.watch on linux for the watcher package.

pkg/watcher/test/directory_watcher/polling_test.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.
+
+import 'package:scheduled_test/scheduled_test.dart';
+import 'package:watcher/watcher.dart';
+
+import 'shared.dart';
+import '../utils.dart';
+
+main() {
+  initConfig();
+
+  // Use a short delay to make the tests run quickly.
+  watcherFactory = (dir) => new PollingDirectoryWatcher(dir,
+      pollingDelay: new Duration(milliseconds: 100));
+
+  setUp(createSandbox);
+
+  sharedTests();
+
+  test('does not notify if the file contents are unchanged', () {
+    writeFile("a.txt", contents: "same");
+    writeFile("b.txt", contents: "before");
+    startWatcher();
+    writeFile("a.txt", contents: "same");
+    writeFile("b.txt", contents: "after");
+    expectModifyEvent("b.txt");
+  });
+
+  test('does not notify if the modification time did not change', () {
+    writeFile("a.txt", contents: "before");
+    writeFile("b.txt", contents: "before");
+    startWatcher();
+    writeFile("a.txt", contents: "after", updateModified: false);
+    writeFile("b.txt", contents: "after");
+    expectModifyEvent("b.txt");
+  });
+}