restore gradientshader.h

Change-Id: Id0cae1420ac78b5fa0d55ad823420463a1e8793a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1124076
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Mike Reed <mike@reedtribe.org>
Reviewed-by: Ben Wagner <bungeman@google.com>
1 file changed