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chromium/third_party/blink/web_tests/paint/invalidation/resources/iframe-gradient-background-scroll-repaint-iframe.html 

<!DOCTYPE html>
<html style="background: linear-gradient(red, blue); overflow:hidden">
<script src="text-based-repaint.js"></script>
<script>
function repaintTest() {
  document.scrollingElement.scrollTop = 20;
}
</script>
<body onload="runRepaintTest()">
<div style="height: 500px"></div>