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

{
  "name": "Platform App Test: <webview> download permission API",
  "manifest_version": 2,
  "description": "Loads a guest which initiates download",
  "version": "1",
  "permissions": [
    "webview"
  ],
  "app": {
    "background": {
      "scripts": ["test.js"]
    }
  }
}