Wrap Directory.watch on Mac OS for the watcher package.

pkg/watcher/lib/src/constructable_file_system_event.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.constructable_file_system_event;
+
+import 'dart:io';
+
+abstract class _ConstructableFileSystemEvent implements FileSystemEvent {
+  final bool isDirectory;
+  final String path;
+  final int type;
+
+  _ConstructableFileSystemEvent(this.path, this.isDirectory);
+}
+
+class ConstructableFileSystemCreateEvent extends _ConstructableFileSystemEvent
+    implements FileSystemCreateEvent {
+  final type = FileSystemEvent.CREATE;
+
+  ConstructableFileSystemCreateEvent(String path, bool isDirectory)
+      : super(path, isDirectory);
+
+  String toString() => "FileSystemCreateEvent('$path')";
+}
+
+class ConstructableFileSystemDeleteEvent extends _ConstructableFileSystemEvent
+    implements FileSystemDeleteEvent {
+  final type = FileSystemEvent.DELETE;
+
+  ConstructableFileSystemDeleteEvent(String path, bool isDirectory)
+      : super(path, isDirectory);
+
+  String toString() => "FileSystemDeleteEvent('$path')";
+}
+
+class ConstructableFileSystemModifyEvent extends _ConstructableFileSystemEvent
+    implements FileSystemModifyEvent {
+  final bool contentChanged;
+  final type = FileSystemEvent.MODIFY;
+
+  ConstructableFileSystemModifyEvent(String path, bool isDirectory,
+          this.contentChanged)
+      : super(path, isDirectory);
+
+  String toString() =>
+    "FileSystemModifyEvent('$path', contentChanged=$contentChanged)";
+}
+
+class ConstructableFileSystemMoveEvent extends _ConstructableFileSystemEvent
+    implements FileSystemMoveEvent {
+  final String destination;
+  final type = FileSystemEvent.MOVE;
+
+  ConstructableFileSystemMoveEvent(String path, bool isDirectory,
+          this.destination)
+      : super(path, isDirectory);
+
+  String toString() => "FileSystemMoveEvent('$path', '$destination')";
+}