chromium/chrome/test/data/extensions/autoplay_iframe/manifest.json

{
  "name": "<iframe> autoplay policy api tests.",
  "version": "1",
  "content_security_policy": "frame-src http://localhost:*/; object-src 'self'; script-src 'self'",
  "manifest_version": 2,
  "browser_action": {
    "default_popup": "main.html"
  }
}