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

{
  "name": "App Test: panel container",
  "version": "1",
  "manifest_version": 2,
  "permissions": [
    "notifications"
  ],
  "app": {
    "launch": {
      "local_path": "empty.html",
      "container": "panel"
    }
  }
}