chromium/ui/file_manager/file_manager/foreground/images/files/ui/expand_more.svg

<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 20 20">
 <polygon points="5.41 6 10 10.945 14.59 6 16 7.522 10 14 4 7.522"/>
</svg>