Hash the gamut of XYZ color spaces, to speed up comparison

Also going to use this to allow caching of GrColorSpaceXforms

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3670

Change-Id: I56ed2dcbdddc22046263f56d68f2d6aea55547c8
Reviewed-on: https://skia-review.googlesource.com/3670
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
8 files changed