LayoutTests/webanimations/offset-anchor-animation-yields-compositing.html

<pre id="results"></pre>
<div id="target" style="width: 100px; height: 100px; background-color: black; offset-path: path('M10,10 H50')"></div>
<script>

testRunner.waitUntilDone();
testRunner.dumpAsText();

document.getElementById("target").animate({
    offsetAnchor: ["0 0", "100% 100%"]
}, 1000 * 60).ready.then(() => {
    document.getElementById("results").innerText = internals.layerTreeAsText(document);
    testRunner.notifyDone();
});

</script>