Add static_asserts for gradient color space values used in SkSL

Bug: skia:13108
Change-Id: I359958e0a34959867473a9376f7fadd4351308af
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/595458
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed