Expose min and max contrast and gamma values publicly

I'm working on a change in Chromium that sets contrast and gamma
in Skia. As part of this, I would like to clamp values to Skia's
range. I initially set this up with hard-coded matching values,
but it will be much cleaner to export them in SkTypes.

I also updated the SkAsssert code to use the publicly exposed values
instead of hard-coded values.

Bug: chromium:1160653
Change-Id: Ib172a68d9546a183c7cc0e443f34f21fb2bd33d7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/820436
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Auto-Submit: Kurt Catti-Schmidt <kschmi@microsoft.com>
2 files changed