chrome/test/data/extensions/platform_apps/optional_permission_request/manifest.json

{
  "name": "Platform App Test: optional permission request test",
  "manifest_version": 2,
  "version": "1",
  "app": {
    "background": {
      "scripts": ["test.js"]
    }
  },
  "optional_permissions": [
    "serial"
  ]
}