int selectedIndex

Source 

@DomName('HTMLSelectElement.selectedIndex')
@DocsEditable()
int get selectedIndex =>
    _blink.BlinkHTMLSelectElement.instance.selectedIndex_Getter_(this);
void selectedIndex=(int value)

Source 

@DomName('HTMLSelectElement.selectedIndex')
@DocsEditable()
set selectedIndex(int value) =>
    _blink.BlinkHTMLSelectElement.instance.selectedIndex_Setter_(this, value);