Disabling Chromium XFCE Power Management Inhibition
This is a verified bug without a patch yet, Launchpad Bug 1600622
One solution that is far from ideal is to block all advertisements with uBlock Origin. Chrome can still inhibit the screensaver, but in this case it seems that whatever is responsible isn't getting through.
Specifically the problem seems to be with GoogleTagServices.com which pulls in this script. If that's blocked by uBlock Origin, you're good and you won't have Power Management Inhibition. If that's not blocked, you'll have problems.