This dirty bit isn't getting set somewhere where it should be, so work around this by
just enabling the dirty bit always. The bit was added here:
https://chromium-review.googlesource.com/c/angle/angle/+/659228
There will be a followup to re-enable this dirty bit once the correctness has been fixed.

Test: https://github.com/KhronosGroup/WebGL/pull/2559
Bug: chromium:792966
Change-Id: I473a60b39eff70e59ab55ff7b74f06fdb0db1305
Reviewed-on: https://chromium-review.googlesource.com/818178
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>