Add FileSystemWatcher class to dart:io.

runtime/bin/file_patch.dart

 // Copyright (c) 2012, 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.
 
 patch class _FileUtils {
   /* patch */ static SendPort _newServicePort() native "File_NewServicePort";
 }
 
 patch class _File {
   /* patch */ static _exists(String path) native "File_Exists";
@@ skipping 24 matching lines @@
   /* patch */ static _writeFrom(int id, List<int> buffer, int start, int end)
       native "File_WriteFrom";
   /* patch */ static _position(int id) native "File_Position";
   /* patch */ static _setPosition(int id, int position)
       native "File_SetPosition";
   /* patch */ static _truncate(int id, int length) native "File_Truncate";
   /* patch */ static _length(int id) native "File_Length";
   /* patch */ static _flush(int id) native "File_Flush";
 }
 
+patch class _FileSystemWatcher {
+  int _watchPath(String path, int events, bool recursive)
+      native "FileSystemWatcher_WatchPath";
+  void _unwatchPath() native "FileSystemWatcher_UnwatchPath";
+  List _readEvents() native "FileSystemWatcher_ReadEvents";
+}
+
 Uint8List _makeUint8ListView(Uint8List source, int offsetInBytes, int length) {
   return new Uint8List.view(source.buffer, offsetInBytes, length);
 }