This allows a replay of the T-Rex offscreen benchmark.

Bug: angleproject:5133
Change-Id: I9998c4785e61a6410863a1cd8a8a569b1e08098a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2446897
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>