chromium/ui/webui/resources/images/icon_filetype_generic.svg

<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20">
  <path fill="#5f6368" d="M11 2l5 5v10a1 1 0 01-1 1H5a1 1 0 01-1-1V3a1 1 0 011-1h6zm-1 2H6v12h8V8h-4V4z"/>
</svg>