@xingnan If there is a clear use case for the "allow-universal-access-from-file-urls" switch in testing, development, or debugging then we can keep it. This is similar to how Chromium enables features to be used in development only and not in production (http://peter.sh/experiments/chromium-command-line-switches/ also exposed via chrome://flags). In production the apps must use the xwalk_hosts Manifest member instead.