chromium/third_party/blink/web_tests/fast/multicol/span/becomes-spanner-with-new-width.html

<!DOCTYPE html>
<p>There should be a green square below, and no red.</p>
<div id="root" style="column-fill:auto; width:300px; height:300px; background:red;">
    <div style="width:100px;">
        <div style="column-span:all; height:300px; background:green;" data-expected-width="300"></div>
    </div>
</div>
<script src="../../../resources/check-layout.js"></script>
<script>
    document.body.offsetTop;
    document.getElementById("root").style.columns = "2";
    checkLayout("#root");
</script>