Spurious screensaver activation while synchronizing the system clock

So, here’s the thing: sometimes, in the first few minutes after I’ve logged into the GNOME desktop, the screensaver activates. I’m pretty sure this happens before the screensaver activation timeout (5 minutes IIRC). Which makes me guess that this is caused by the screensaver idle counter being confused by the system time changing under its feet, due to our time synchronization process.

I’ve been experiencing this regularly for a while, but have been too lazy until now to report it properly. I assume that I’m not an isolated example, and that other people suffer from it too. This behaviour is surprising, and I expect that new users will be confused if they have to learn how to exit the screensaver that early in their initial Tails experience.

I propose we disable the screensaver activation entirely for now (and revert fc5155af587d3f1161db8a7b54a3dd7c9bd73406 since the default settings will then fit the needs of the test suite): it can potentially confuse any user in the general case, and the kind of people who already use the (unsupported so far) screen locking feature should be able to re-enable this timeout if they desire so.

Later on, whenever the screen locking implementation is completed, if the idea is to have it self-activate based on this timeout, then this activation system should probably be disabled during time synchronization, otherwise we’ll be re-introducing this bug.

Related issues

• Related to #5684 (closed)
• Related to #5799 (closed)

Original created by @intrigeri on 12098 (Redmine)