Cache GrColorSpaceXforms

Even with a modest cache, we're going to get nearly 100% hit rate
for typical usage scenarios. I'm hoping to avoid the special case
caching of sRGB -> destination, and just rely on the more general
mechanism.

Yes, this is yet-another cache class. I wanted to use one of many
that are laying around, but couldn't find a good fit. On the plus
side, it's not much code.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3726

Change-Id: I943be5c99f0d691a87ffe8c5bc3067a8eb491fc2
Reviewed-on: https://skia-review.googlesource.com/3726
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
2 files changed