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

Source 

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