1. DomName('SVGPathSegList.insertItemBefore')
  2. DocsEditable()
PathSeg insertItemBefore(PathSeg newItem, int index)

Source 

@DomName('SVGPathSegList.insertItemBefore')
@DocsEditable()
PathSeg insertItemBefore(PathSeg newItem, int index) => wrap_jso(_blink.BlinkSVGPathSegList.instance.insertItemBefore_Callback_2_(unwrap_jso(this), unwrap_jso(newItem), index));