firefox/testing/web-platform/tests/css/css-paint-api/valid-image-after-load.https.html

<!DOCTYPE html>
<html class="reftest-wait">
<link rel="help" href="https://drafts.css-houdini.org/css-paint-api/">
<link rel="match" href="valid-image-after-load-ref.html">
<style>
    #output {
        width: 100px;
        height: 100px;
        background-color: red;
    }
</style>
<script src="/common/reftest-wait.js"></script>
<body>
<div id="output"></div>

<script id="code" type="text/worklet">
registerPaint('green', class {
    paint(ctx, geom) {
        ctx.fillStyle = 'green';
        ctx.fillRect(0, 0, geom.width, geom.height);
    }
});
</script>

<script>
var blob = new Blob([document.getElementById('code').textContent],
                    {type: 'text/javascript'});
var frame_cnt = 0;
CSS.paintWorklet.addModule(URL.createObjectURL(blob)).then(function() {
    var el = document.getElementById('output');
    el.style.backgroundImage = 'paint(green)';
    requestAnimationFrame(function() {
        takeScreenshot(frame_cnt);
    });
});
</script>
</body>
</html>