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chromium/third_party/blink/web_tests/fast/forms/suggestion-picker/time-suggestion-picker-appearance-with-scroll-bar.html 

<!DOCTYPE html>
<meta name=fuzzy content="maxDifference=0-3; totalPixels=0-1000">
<script src="../../../resources/testdriver.js"></script>
<script src="../../../resources/testdriver-vendor.js"></script>
<script src="../resources/picker-common.js"></script>

<body style="background-color: #eeffff;">
<input type=time value="12:31" list="suggestions" style="width: 100px;">
<datalist id=suggestions>
  <option label="Now">01:01</option>
  <option>01:02</option>
  <option>01:03</option>
  <option>01:04</option>
  <option>01:05</option>
  <option>01:06</option>
  <option>01:07</option>
  <option>01:08</option>
  <option>01:09</option>
  <option>01:10</option>
  <option>01:11</option>
  <option>01:12</option>
  <option>01:13</option>
  <option>01:14</option>
  <option>01:15</option>
  <option>01:16</option>
  <option>01:17</option>
  <option>01:18</option>
  <option>01:19</option>
  <option>01:20</option>
  <option>01:21</option>
</datalist>

<script>
  window.onload = openPickerAppearanceOnly(document.querySelector('input'),() => {
    internals.pagePopupWindow.focus();
    eventSender.keyDown('ArrowDown');
  });
</script>