A knowledge base article about ChromeOS on Berkeley-Visitor displays Untrusted Site on connecting.gstatic.com provided by the UC Berkeley IT Service Hub - Knowledge Portal
Some users of Berkeley-Visitor will see a "This site is not safe" error on a popup for connection.gstatic.com when attempting to connect connect. This error relates to the Chrome setting "Always use secure connections".
The way a Berkeley-Visitor, and most open Wi-Fi Captive Portals, work is to redirect all http traffic to a redirect page, that redirect page then forwards the user to the Welcome to Wi-Fi terms page. The first step uses a non-encrypted HTTP session, and is usually too fast for the user to see.
In the case of the Chrome Browser on ChromeOS the page does not automatically redirect. This is because that first page is not encrypted, and ChromeOS won't let you continue the portal until you've allowed the browser to finish loading the non-encrypted page.
If you see this message, just click on the Continue button and the Welcome page will load. There are no security concerns because no data is transmitted to the redirect page.