Detect when we can skip clamps on gamut transforms.

Detect when we can skip clamps on gamut transforms.

This is the same logic from the matrix color filter, scaled down from 4x5 to 3x4.
I'm seeing cases in GMs where we can skip clamps in both directions, but never both together.

Change-Id: I515c5e207d35ed23f1e267d55460fe4d41e1a8f1
Reviewed-on: https://skia-review.googlesource.com/5456
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>