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chromium/third_party/blink/web_tests/fast/multicol/dynamic/float-becomes-spanner.html 

<!DOCTYPE html>
<p>Turn a float into a column spanner.</p>
<p>Below there should be a blue <em>square</em>.</p>
<div style="-webkit-columns:3; column-fill:auto; width:100px; height:100px;">
    <div id="spanner" style="float:left; width:100%; height:100px; -webkit-column-span:all; background:blue;"></div>
</div>
<script>
    document.body.offsetTop;
    document.getElementById("spanner").style.cssFloat = "none";
</script>