chromium/src/third_party/blink/web_tests/fast/workers/resources/throw-on-message-worker.js

self.onerror = function(evt) {
    postMessage('error');
    return true;
}

self.onmessage = function(evt) {
    if (evt.data === "first")
        throw Error();
    else
        postMessage(evt.data);
}