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chromium/third_party/blink/web_tests/media/media-controls-grey-scrubber.html 

<!DOCTYPE html>
<script src="media-controls.js"></script>
<body>
<!--
  A <video> object with a valid source and
  preload set to "none" should show a greyed
  timeslider element.
 -->
<div><video controls preload="none" src="content/test.mp4" ></video></div>
<script>
const video = document.querySelector('video');
enableTestMode(video);
</script>
</body>