The sampler returns colors with components in the range 0-255.

Bug: chromium:963595
Change-Id: I7030ab9da6e0803e3aaf8aef4691ce7276636b10
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1617778Reviewed-by: Kimmo Kinnunen FI <kkinnunen@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>