Condition evaluation checks are fairly expensive, and turns out we
repeat a lot of checks. All those checks are also done in a single
thread.

With this cache on my workstation, a noop gclient runhooks takes 9.5s.
Without one, it takes 26.2s.

R=gavinmak@google.com

Change-Id: Ie00b7af22cd124d08dd9fd218de77b34bbdfe6ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3309823Reviewed-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>