chromium/chrome/test/data/extensions/platform_apps/web_view/background/manifest.json

{
  "name": "Platform App Test: <webview> background page access",
  "manifest_version": 2,
  "version": "1",
  "permissions": [
    "webview"
  ],
  "app": {
    "background": {
      "page": "background.html"
    }
  }
}