Correctly pass errors to the stream, when watching file system entities.

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 52 matching lines @@
     }
     _controller = new StreamController.broadcast(onListen: _listen,
                                                  onCancel: _cancel);
   }
 
   void _listen() {
     int socketId;
     try {
       socketId = _watchPath(_path, _events, identical(true, _recursive));
     } catch (e) {
-      throw new FileSystemException(
-          "Failed to watch path",
-          _path,
-          e);
+      _controller.addError(new FileSystemException(
+          "Failed to watch path", _path, e));
+      _controller.close();
+      return;
     }
     var socket = new _RawSocket(new _NativeSocket.watch(socketId));
     _subscription = socket.expand((event) {
       bool stop = false;
       var events = [];
       var pair = {};
       if (event == RawSocketEvent.READ) {
         String getPath(event) {
           var path = _path;
           if (event[2] != null) {
@@ skipping 71 matching lines @@
 
   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);
 }