chromium/third_party/blink/web_tests/fast/multicol/composited-layer.html

<!DOCTYPE html>
<style>
#multicol {
    -webkit-column-count: 2;
    -webkit-column-gap: 0;
    column-count: 2;
    column-gap: 0;
    width: 200px;
    height: 100px;
    will-change: transform;
}

.filler {
    width: 100px;
    height: 100px;
}
</style>
<div id="multicol">
    <div class="filler"></div>
    <div class="filler"></div>
</div>
<div id="layers"></div>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

if (window.internals)
    document.getElementById("layers").innerText = internals.layerTreeAsText(document);
</script>