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chromium/third_party/blink/web_tests/compositing/overflow/composited-scroll-background-obscured-expected.html 

<!doctype HTML>
<div id="target" style="height: 100%; overflow-y:scroll; background-color: yellow; will-change: transform; width: 200px; height: 200px;">
  <div style="width: 200px; height: 400px;"></div>
</div>
<script>
target.scrollTop = 200;
</script>