I created a ButtonInputWidget through HTMLForm:
$form->addButton( 'deny', $this->msg( 'globalrenamequeue-request-deny-text' )->text(), 'mw-renamequeue-deny', array( 'class' => 'mw-globalrenamequeue-submit', 'flags' => array( 'destructive', 'primary' ), 'infusable' => true, ) );
When I infuse this on the client side (OO.ui.infuse('mw-renamequeue-deny')), it loses the mw-globalrenamequeue-submit class.