Implement clamp stages in lowp raster pipeline
Implement clamp stages in lowp raster pipeline

When these were first written, it was true that we couldn't get colors
out of gamut. That's not generally true, though, particularly as we
remove clamping to in-gamut before blending (to make things consistent
with skvm and GPU).

Bug: skia:13715
Change-Id: Id3bcaa58273b2ba986464100ad8df4cf9a671271
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/578499
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Reviewed-by: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia