This is based on recent discussion in Khronos, though public specs
have not yet been updated to reflect this.

BUG=angleproject:2388
TEST=angle_unittests

Change-Id: I66a0d03b3c2bb9740772a813b543f8f6c6bb2a28
Reviewed-on: https://chromium-review.googlesource.com/947977Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>