<!DOCTYPE html>
<html>
    <head>
        <title>Changing from paged-x to paged-y</title>
        <script>
            function test() {
                document.body.offsetTop; // trigger layout
                document.body.style.overflow = 'paged-y';
                document.body.style.overflow = '-webkit-paged-y';
            }
        </script>
    </head>
    <body style="overflow:-webkit-paged-x; overflow:paged-x;" onload="test()">
        <div style="height:150vh;">
            There should be a vertical scrollbar on this page.
        </div>
    </body>
</html>