Code review comment for lp://qastaging/~mir-team/mir/public-cookie-api

+ typedef struct MirCookie MirCookie;

Not needed (at the moment at least), and also may conflict with mir::cookie::MirCookie.

- virtual MirCookie timestamp_to_cookie(uint64_t const& timestamp) = 0;

A *Cookie*Factory that doesn't create cookies seems strange.

Needs discussion/fixing