We were saving "width" bytes instead of "width * pixelSize". This was
causing incorrect rendering in T-Rex and Manhattan.

Bug: angleproject:4488
Change-Id: Ib5d38aaf813fb26905aedc155cc13b9d1597ec4c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2109336Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>