The Mac mixins were updated. Ideally we could do this automatically on
Chromium rolls.

Bug: angleproject:5114
Change-Id: I412e227193e7a6503c04dee5df6bb2a4cf1cc1f5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2857597Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>