Fixed by:
https://swiftshader-review.googlesource.com/c/SwiftShader/+/50008

The specific flaky crash was reported here:
https://bugs.chromium.org/p/angleproject/issues/detail?id=4482#c15

Bug: angleproject:4482
Change-Id: Ia77b4b094446d14866bee5fd461a0a4eea52491e
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2521237Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>