We collect instance type statistics in FatalProcessOutOfMemory into an
array, which is allocated to the max instance type value. While we want
to leave space to ensure new instance types do not affect constants in
the API, we can be more frugal.

We currently serialize 350 maps into the startup/context snapshot.  Even
if we assign a distinct instance type to each of these maps, we would
still have more than enough to spare with this change.

R=ulan@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I3e583c2c8da3342e9132d96046b5d80cd41afd72
Reviewed-on: https://chromium-review.googlesource.com/842542
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50302}