file method

Implementation

@JSName('file')
Future<File> file() {
  var completer = new Completer<File>();
  _file(
    (value) {
      applyExtension('File', value);
      completer.complete(value);
    },
    (error) {
      completer.completeError(error);
    },
  );
  return completer.future;
}