chromium/third_party/blink/web_tests/external/wpt/workers/modules/resources/post-message-on-load-worker.js

if ('DedicatedWorkerGlobalScope' in self &&
    self instanceof DedicatedWorkerGlobalScope) {
  postMessage('LOADED');
} else if (
    'SharedWorkerGlobalScope' in self &&
    self instanceof SharedWorkerGlobalScope) {
  self.onconnect = e => {
    e.ports[0].postMessage('LOADED');
  };
}