Make SkColorSpaceXform an SK_API

TBR=reed@google.com
BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3585

Change-Id: I8efaf7c46e0d600bb1bb92e39014db8c4a8d25d1
Reviewed-on: https://skia-review.googlesource.com/3585
Commit-Queue: Matt Sarett <msarett@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
1 file changed