fit-content-change-available-size-blocks.html

<!DOCTYPE html>
<div id="container" style="width:500px;">
  <div id="stf" style="width:fit-content;"></div>
</div>
<script src="../resources/runner.js"></script>
<script>
  var stf = document.getElementById("stf");

  for (var i = 0; i < 10000; i++) {
      var child = document.createElement("div");
      child.style.width = "100px";
      child.style.height = "1px";
      stf.appendChild(child);
  }

  var container = document.getElementById("container");
  var style = container.style;

  function test() {
      style.width = "400px";
      PerfTestRunner.forceLayout();
      style.width = "500px";
      PerfTestRunner.forceLayout();
  }

  PerfTestRunner.measureRunsPerSecond({
      description: "Measures performance of relayout of a container with many auto fit-content children.",
      run: test
});
</script>
</html>

chromium/third_party/blink/perf_tests/layout/fit-content-change-available-size-blocks.html