<!DOCTYPE html>
<script src="../../../resources/run-after-layout-and-paint.js"></script>
<script>
if (window.internals) {
  internals.settings.setPreferCompositingToLCDTextEnabled(true);
  internals.useMockOverlayScrollbars();
}

if (window.testRunner)
  testRunner.waitUntilDone();

runAfterLayoutAndPaint(function() {
  document.getElementById('content').style.height = '250px';
  runAfterLayoutAndPaint(function() {
    document.getElementById('content').style.height = '150px';
    document.body.appendChild(document.createTextNode('Finished.'));
  }, true);
});
</script>

Tests a float changes using composited scrolling. Passes if the green square is always visible.<p>
To test manually, use command line switches --enable-prefer-compositing-to-lcd-text --enable-features=OverlayScrollbar
<div style="height: 200px">
  <div style="float: left; width: 300px; height: 100%; overflow: auto; background-color: green">
    <div id="content" style="height: 150px"></div>
  </div>
</div>