chromium/chrome/test/data/extensions/api_test/messaging/on_pagehide/manifest.json

{
  "name": "send message on pagehide",
  "version": "1.0",
  "manifest_version": 2,
  "description": "Sends a message on tab unload",
  "background": {
    "persistent": true,
    "scripts": ["test.js"]
  },
  "content_scripts": [{
    "matches": ["*://*/*"],
    "js": ["content_script.js"]
  }]
}