Recover the original primaries (using CHAD) when emitting gamut diagrams

We were extracting the primaries from the D50 adapted matrix, but for
spaces with a different white point, the resulting primaries didn't
match published values. The correct answer is to first undo the Bradform
transform.

Change-Id: I6ed169bd220209dfd77ee4455112a4cc20fc3636
Reviewed-on: https://skia-review.googlesource.com/129626
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed