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

<!DOCTYPE html>
<title>Test shared 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 SharedWorker('resources/shared-worker-timezonechange.js', 'name');
    const msg1 = await new Promise(r => worker.port.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.port.onmessage = r);
    assert_equals(msg2.data, "SUCCESS");
}, "Test a shared worker handles ontimezonechange event.");
</script>