remove plus clamp

Clamping for plus mode should happen only as the destination format
requires it, or as a consequence of the limited range we're holding
colors in the pipeline, or because non-normalized alpha is nuts.

So I've taken away the clamp on float rgb, keeping it on lowp to stay
in its legal range, and on float alpha because it's crazy not to.

Open questions:
  - also clamp alpha to zero?
  - what do we do with alpha <0 or >1 in general, beyond plus?

Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Change-Id: I15660ce55cc393e312f18ffdc13bbfdef08ac6e0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201040
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed