third_party/blink/perf_tests/paint/gap-decorations-multicol.html

<!DOCTYPE html>
<script src="../resources/runner.js"></script>
<script src="resources/paint.js"></script>
<div id="container" style="columns:10000; column-gap:3px; column-rule: 1px solid red; column-fill:auto; height:100px;">
    <div style="height:250000px;"></div>
    <div style="height: 10px; column-span: all;"></div>
    <div style="height:250000px;"></div>
    <div style="height: 10px; column-span: all;"></div>
    <div style="height: 250000px;"></div>
</div>
<script>
  // Measure paint / pre-paint performance of a multicol container with many
  // columns and gap decorations.

  var wide = false;

measurePaint({
  run: function() {
    container.style.width = wide ? "600px" : "700px";
    wide = !wide;
  },
});
</script>