Add gamma function to skcms.

This results in less work than applying a complete transfer
function.

Change-Id: I880f9221b780b252893860a78f5e4a18e83d0918
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/771486
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
2 files changed