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chromium/third_party/blink/web_tests/timezonechange/worker-timezonechange.html 

<!DOCTYPE html>
<title>Test worker handle ontimezonechange event.</title>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<script>
promise_test(async t => {
  const worker = new Worker('resources/worker-timezonechange.js');
  const msg1 = await new Promise(r => worker.onmessage = r);
  assert_equals(msg1.data, "READY");
  // Once we know the worker is ready, we change the timezone.
  internals.setSystemTimeZone("Asia/Taipei");
  const msg2 = await new Promise(r => worker.onmessage = r);
  assert_equals(msg2.data, "SUCCESS");
}, "Test a dedicated worker handles ontimezonechange event.");
</script>