change gradients4f to use srgb

Bug: skia:
Change-Id: I49d6fab8ab9ae9accea2cab9e85f9a4e9cac50e8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/198164
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed