chrome/browser/resources/side_panel/shared/sp_icons.html

<cr-iconset name="sp" size="16">
  <svg>
    <defs>
      <g id="filter-list" viewBox="0 0 24 24">
        <path d="M3 6v2h18V6H3Zm7 12h4v-2h-4v2Zm8-5H6v-2h12v2Z"></path>
      </g>
    </defs>
  </svg>
</cr-iconset>