LayoutTests/fast/repaint/leftover-after-shrinking-content.html

<style>
body {
  width: 400px;
}
span {
  font-family: Ahem;
  font-size: 50px;
}
</style>
<!-- PASS if no repaint issue after shrinking the text content -->
<span id=content>text content</span>
<script>
document.designMode = "on";
let counter = 0;
document.body.addEventListener("beforeinput", e => {
  if (++counter == 2) {
    content.style.fontSize = "10px";
    document.body.offsetHeight;
  }
});

document.body.offsetHeight;

if (window.testRunner) {
  testRunner.dumpAsText();
  testRunner.waitUntilDone();
}

setTimeout(function() {
  document.body.focus();
  document.execCommand("insertText", false, "1");

  setTimeout(function() {
    if (window.internals)
        internals.startTrackingRepaints();
    document.execCommand("insertText", false, "2");
    document.body.offsetTop;

    if (window.internals) {
      var repaintRects = internals.repaintRectsAsText();
      internals.stopTrackingRepaints();
      var pre = document.createElement('pre');
      document.body.appendChild(pre);
      pre.innerHTML = repaintRects;
    }
    if (window.testRunner)
      testRunner.notifyDone();
  }, 10);
}, 10);
</script>