The scaling factors ensure that the components are rounded correctly even after
alpha blending, which may multiply colors by colors.

Bug 24332884

Change-Id: Ib75602e89996b2fd1a319a132a681295fb2a18a6
Reviewed-on: https://swiftshader-review.googlesource.com/5048Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>