Add error handling when initializing the file system watcher

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 81 matching lines @@
 
   Stream get stream => _broadcastController.stream;
 
   void _listen() {
     if (_id == null) {
       try {
         _id = _initWatcher();
         _newWatcher();
       } catch (e) {
         _broadcastController.addError(new FileSystemException(
-            "Failed to initialize file system entity watcher"));
+            "Failed to initialize file system entity watcher", null, e));
         _broadcastController.close();
         return;
       }
     }
     var pathId;
     try {
       pathId = _watchPath(_id, _path, _events, _recursive);
     } catch (e) {
       _broadcastController.addError(new FileSystemException(
           "Failed to watch path", _path, e));
@@ skipping 248 matching lines @@
   void _pathWatchedEnd() {
     _subscription.cancel();
     _controller.close();
   }
 }
 
 
 Uint8List _makeUint8ListView(Uint8List source, int offsetInBytes, int length) {
   return new Uint8List.view(source.buffer, offsetInBytes, length);
 }