chromium/chrome/test/data/extensions/platform_apps/web_view/post_message/basic/manifest.json

{
  "name": "Platform App Test: <webview> basic postMessage",
  "manifest_version": 2,
  "version": "1",
  "permissions": ["webview"],
  "app": {
    "background": {"scripts": ["test.js"]}
  }
}