Revert "Remove deadcode for sRGB image shading."

This reverts commit 51f6a0f89e55b2c0f102aa7963320a23c586e71d.

Reason for revert: try to fix chrome roll

Original change's description:
> Remove deadcode for sRGB image shading.
> 
> Change-Id: I9d98da67d97b64ab55cf44b9ae447882dccda1ca
> Reviewed-on: https://skia-review.googlesource.com/20695
> Reviewed-by: Mike Klein <mtklein@chromium.org>
> Commit-Queue: Herb Derby <herb@google.com>

TBR=mtklein@chromium.org,mtklein@google.com,herb@google.com,reed@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I90409a08409177d9dc3b094d736af0fdaf7d6cdd
Reviewed-on: https://skia-review.googlesource.com/20824
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
42 files changed