Reduces shard time from 50+ min to <10 min per shard.

Bug: angleproject:5966
Change-Id: Ia230d71a66ac9a273a10e0389cc04d8c5737bc4a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2915566
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>