chromium/chrome/test/data/banners/manifest_one_maskable.json

{
  "name": "Manifest test app",
  "icons": [
    {
      "src": "image-512px.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "maskable"
    }
  ],
  "start_url": "manifest_test_page.html",
  "display": "standalone",
  "orientation": "landscape"
}