code: func (s *DriveService) Stat(ctx context.Context, title string) (int64, error) {
  	file, err := s.Get(ctx, title)
  	if err != nil || file == nil {
  		return 0, err
  	}
  	return file.FileSize, err
  }
docs: // Stat retrieves file metadata and returns
  // file size. Returns error if file is not found.