commit 9b79b2447671f52e2e64785f03f0f3989621cb15
author Eric Orth <ericorth@chromium.org> Tue Jul 20 20:53:18 2021
committer Chromium LUCI CQ <chromium-scoped@luci-project-accounts.iam.gserviceaccount.com> Tue Jul 20 20:53:18 2021
tree af62303ecf5c0ffc667fb21e6bf81bdd69b9563e
parent 24a51efd20ebe5f9d0d8a696893f359e3667974a

Create ProxyHostResolverCache

Serves as a replacement for the net::HostCache usage in
/services/proxy_resolver.

Nice features of this cache over net::HostCache:
* Divorced from net::HostCache to allow that class to make its own
  changes with less dependencies to worry about.
* More performant (lg(n)) eviction when full.  net::HostCache is more
  complicated and always needs to do a full linear scan of the entire
  cache.
* Stale entries always removed when found. net::HostCache needs to deal
  with a lot more complications around keeping and sometimes using
  stale entries.
* Key/entry types specialized to proxy usage instead of having a bunch
  of unused fields and requiring some conversions.
* TTL logic better encapsulated instead of making callers deal with
  passing in times and deciding TTL.
* Skips lots of net::HostCache functionality that was completely
  unnecessary for proxy script resolution usage.

Old logic used default cache size from
net::HostCache::CreateDefaultCache(), which has a max size of 100 or
1000 depending on ENABLE_BUILT_IN_DNS. But this code's caching needs
has no relation to whether or not the built-in DNS resolver is being
used, so I arbitrarily split the difference in setting the new cache's
max size to 500.

Also worth noting that the new cache is only used for positive results.
HostResolverMojo previously saved error results into its
net::HostCache, but it did so with a TTL of 0, resulting in the entry
being stale and unusable as soon as any measurable amount of time has
passed.

Fixed: 1229361
Change-Id: I02f2c37f3a3419997d65d4ab90a0df31f9a23c07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3032014
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Orth <ericorth@chromium.org>
Cr-Commit-Position: refs/heads/master@{#903641}