AppCache is now removed from insecure contexts. AppCache is a powerful feature that allows offline and persistent access to an origin, which is a powerful privilege escalation for an XSS. This will remove that attack vector by only allowing it over HTTPS. This feature was deprecated in Chrome 67.
Docs: https://www.chromium.org/Home/chromium-security/deprecating-powerful-features-on-insecure-origins https://w3c.github.io/webappsec-secure-contexts/