Upstream chromium switched away from master_preferences to
initial_preferences for their first run config override file - I think
sometime around chromium 105. We had been hardcoding
/etc/chromium/master_preferences in the old version of the
debianization/master-preferences patch, and had only noticed that the
the default changed circa chromium 112. We adjusted the patch to accept
both config file locations.

However, with chromium 115, the logic to check for both config file
locations moved from the same function that our
master-preferences.patch modifies, to a completely different directory
& file. Thus, when upstream finally drops support for
master_preferences, we're likely not going to even notice until users
start complaining.

Our packaging also still creates /etc/chromium/master_preferences. So
the first thing we need to do is switch that to initial_preferences.
The next thing we need to do is to warn users about the change, in case
they're supplying their own initial config override. A NEWS entry seems
like overkill considering the vast majority of users don't care about
it, so I'm thinking what would make the most sense would be to either
modify debianization/master-preferences.patch to spit out a warning if
master_preferences is detected, or have the package's postinst script
check for the file and spit out a warning. The former option would only
be seen the first time chromium is run, while the latter would be seen
every time an upgrade is done (and could automatically rename
master_preferences to initial_preferences if initial_preferences
doesn't already exist).

fwiw i'd appreciate a NEWS.Debian entry as well, it's too easy to miss
messages from postinst - much better to have it somewhere people can read
at their convenience (and apt-list-changes send the NEWS by email) than
scrolling by - i imagine unattended-upgrades doesnt even show people those
messages anyway

(and i say this as someone who very likely doesnt need to take any action
as a result )