Fixes for SkColorLookUpTable::interp3D

(1) Fix subtle comparison bug so we interpolate the proper tetrahedral.
(2) Add new comments - the clamp is necessary.
(3) SkCSXformPrintf requires an extra friend class to compile.

BUG:668784

Change-Id: Id1a5c561f23ccfe25e141b8490cddee4c2482326
Reviewed-on: https://skia-review.googlesource.com/5238
Reviewed-by: Robert Aftias <raftias@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
tree: f7fca5106ed573a8477546ddca0ddc51cacb6b2a
  1. recipe_modules/
  2. recipes.py
  3. recipes/