Test sRGB with non-linear blending using new "srgbnl" sink

BUG=skia:

Change-Id: Ief7516c1505f8e447f83121ed4ba75b9fa9ba75b
Reviewed-on: https://skia-review.googlesource.com/8976
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
13 files changed