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chromium/third_party/blink/web_tests/paint/invalidation/subpixel-shadow-move.html 

<!DOCTYPE html>
Passes if there is no residue when the black bar moving up.
<div id="target"
    style="position: relative; top: 50px; width: 100px; height: 100px; box-shadow: 0 8.2px 0 0 black"></div>
<script src="../../resources/run-after-layout-and-paint.js"></script>
<script>
if (window.testRunner)
  testRunner.waitUntilDone();

var target_top = 50;
function test() {
  target_top -= 0.25;
  console.log(target_top);
  target.style.top = target_top + 'px';
  if (window.testRunner && target_top <= 40) {
    testRunner.notifyDone();
  } else {
    runAfterLayoutAndPaint(test);
  }
}
onload = test;
</script>