Fix gainmap shader when the base image is HDR.

See the section called "How to Scale the Gain Map" of the
Gain Map Specification at
https://helpx.adobe.com/camera-raw/using/gain-map.html

Original author: ccameron@chromium.org

Change-Id: I3ee0ce746b77d00d9face75e6f04c11442885580
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/716497
Commit-Queue: Maryla Ustarroz-Calonge <maryla@google.com>
Reviewed-by: Christopher Cameron <ccameron@google.com>
1 file changed