Fix type-error from previous commit.

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 _File {
   /* patch */ static _exists(String path) native "File_Exists";
   /* patch */ static _create(String path) native "File_Create";
   /* patch */ static _createLink(String path, String target)
       native "File_CreateLink";
   /* patch */ static _linkTarget(String path) native "File_LinkTarget";
@@ skipping 32 matching lines @@
   final int pathId;
   final String path;
   final int events;
   int count = 0;
   _WatcherPath(this.pathId, this.path, this.events);
 }
 
 
 patch class _FileSystemWatcher {
   static int _id;
-  static final Map<int, _FileSystemWatcherPath> _idMap = {};
+  static final Map<int, _WatcherPath> _idMap = {};
 
   final String _path;
   final int _events;
   final bool _recursive;
 
   _WatcherPath _watcherPath;
 
   StreamController _broadcastController;
 
   /* patch */ static Stream<FileSystemEvent> watch(
@@ skipping 286 matching lines @@
   void _pathWatchedEnd() {
     _subscription.cancel();
     _controller.close();
   }
 }
 
 
 Uint8List _makeUint8ListView(Uint8List source, int offsetInBytes, int length) {
   return new Uint8List.view(source.buffer, offsetInBytes, length);
 }