chromium/third_party/blink/web_tests/html/selectlist/selectlist-viewport.html

<!DOCTYPE html>
<html lang="en">
<script src='../../resources/testharness.js'></script>
<script src='../../resources/testharnessreport.js'></script>
<script src="../../resources/testdriver.js"></script>
<script src="../../resources/testdriver-actions.js"></script>
<script src="../../resources/testdriver-vendor.js"></script>

<selectlist id="selectList">
  <option>one</option>
  <option>two</option>
  <option>three</option>
</selectlist>

<script>
function clickOn(element) {
  const actions = new test_driver.Actions();
  return actions.pointerMove(0, 0, {origin: element})
    .pointerDown({button: actions.ButtonType.LEFT})
    .pointerUp({button: actions.ButtonType.LEFT})
    .send();
}

promise_test(async () => {
  if (window.internals) {
      // Regression test for crbug.com/1252600
      // On mobile, <meta name="viewport"> can trigger a layout pass when
      // querying FrameView size. This test ensures that that this doesn't
      // cause a re-entrant layout when opening the <selectlist> popup.
      // Since desktop browsers ignore <meta name="viewport">, set viewport
      // using internals.settings.
      internals.settings.setViewportEnabled(true);
      internals.settings.setViewportMetaEnabled(true);
  }
  const selectList = document.getElementById("selectList");
  assert_false(selectList.open);
  await clickOn(selectList);
  assert_true(selectList.open);
}, "select should open successfully if viewport is enabled");
</script>