chromium/third_party/blink/web_tests/external/wpt/workers/WorkerPerformanceNow.html

<!DOCTYPE html>
<html>
<head>
<title>performance.now in dedicated workers</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
</head>
<body>
<script>
async_test(function(t) {
  const worker = new Worker('support/WorkerSendingPerformanceNow.js');
  worker.onmessage = t.step_func_done(event => {
    const results = event.data;
    assert_equals(results.length, 4);
    assert_equals(results[0], 'undefined',
      'workerStart not defined on the Worker object');
    assert_equals(results[1], 'object', "self.performance is defined");
    assert_equals(results[2], 'function', "self.performance.now is defined");
    assert_greater_than(results[3], 0, "Time in the worker should be positive");
    assert_greater_than(window.performance.now(), results[3], "Time in the worker should be before the current time in the main document");
  });
  worker.postMessage('');
}, 'performance.now() exists in dedicated workers and reports reasonable times');
</script>
</body>
</html>