Instead of passing potentially-dynamic strings over the IPDL interface,
pass an integer which corresponds to one of a fixed set of static
strings. (This is basically an enum with more steps -- or with fewer
steps, depending on which side of it you're standing on.)
This ensures that the set of possible location-strings is fixed, which
in turn both ensures that aggregation of telemetry stays relatively
simple and guards against accidental leakage of PII thereinto. (Or,
alternatively and equivalently, this minimizes the code region that
data-review needs to consider once the location string is reported to
telemetry.)
Note that we do not yet actually report the location-string via
telemetry; that's planned to occur in bug 1884221.
Differential Revision: https://phabricator.services.mozilla.com/D205169
078903e2e0