bug#56546: 29.0.50; unbounded RAM comsumption when displaying images

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: mail@jao.io,  56546@debbugs.gnu.org
> Date: Thu, 14 Jul 2022 12:01:16 +0200
> 
> Lars Ingebrigtsen <larsi@gnus.org> writes:
> 
> > But we can at least include the size of the main data blob (e.g., the
> > .webp data itself); we know the size of that for all the anim caches.
> 
> No, not even that -- the cache is pretty opaque in general.  Hm...

Don't we allocate memory for the cached stuff?  If so, we could count
the bytes there, and record them in the cache itself.