1. @DomName('SVGNumberList.insertItemBefore')
  2. @DocsEditable()
Number insertItemBefore(Number newItem, int index)

Source 

@DomName('SVGNumberList.insertItemBefore')
@DocsEditable()
Number insertItemBefore(Number newItem, int index) =>
    _blink.BlinkSVGNumberList.instance
        .insertItemBefore_Callback_2_(this, newItem, index);