chromium/chrome/test/data/extensions/api_test/messaging/on_pagehide/content_script.js

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

window.addEventListener('pagehide', function() {
  chrome.runtime.sendMessage('Unloading');
});

chrome.test.sendMessage('listening');