servo/tests/wpt/web-platform-tests/screen-orientation/resources/sandboxed-iframe-locking.html

<script>
let msg = "";
screen.orientation.lock("portrait-primary")
.then(() => {
  msg = screen.orientation.type;
}).catch(error => {
  msg = error.name;
}).finally(() => {
  parent.window.postMessage(msg, "*");
});
</script>