Re: Lower max size of HTTP cache?

Let's move the telemetry for working set size issue to Bugzilla:

   https://bugzilla.mozilla.org/show_bug.cgi?id=708436

> So it sounds like the slowdown issues are all fixed? Are there any
> other reasons why we would want to decrease the size?

1) There's some (isolated, anecdotal) telemetry data that indicates
there *might* be slow starts (>8sec) that aren't related to
cache.trash (we got really long telemetry for opening the cache w/o
getting telemetry for the cache.trash deletion time.  It was just one
data point, though, and the aggregate telemetry stats for cache
startup aren't bad).

2) When a user clicks "clear recent history" we blow away the whole
disk cache (we don't have a way to remove items by time added).
Michal tells me we don't use nsDeleteDir for this (which would be
async): instead we synchronously evict the entire cache :(   I'm not
sure if that's fixable (the issue is what to do with loads that are
using the cache as the user hits the button IIRC), but assuming it's
not in a short time frame, that might be enough to merit keeping the
size under a gig.

Jason