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chromium/third_party/blink/web_tests/external/wpt/layout-instability/transform-change.html 

<!DOCTYPE html>
<title>Layout Instability: no layout shift for transform change</title>
<link rel="help" href="https://wicg.github.io/layout-instability/" />
<style>
body { margin: 0; }
#transformed { position: relative; transform: translateX(20px); width: 100px; height: 100px; background: blue; }
#child { width: 400px; height: 400px; }
</style>
<div id="transformed">
  <div id="child"></div>
</div>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/util.js"></script>
<script>

promise_test(async () => {
  const watcher = new ScoreWatcher;

  // Wait for the initial render to complete.
  await waitForAnimationFrames(2);

  // Modify the transform, for which no shift should be reported.
  document.querySelector("#transformed").style = "transform: translateY(100px)";
  // Change size of child, for which no shift should be reported, either.
  document.querySelector("#child").style = "width: 300px";

  await waitForAnimationFrames(2);
  // No shift should be reported.
  assert_equals(watcher.score, 0);
}, 'no layout shift for transform change');

</script>