Start supplying random color space xforms to FP tests

Added helper to create random GrColorSpaceXforms in unit tests, and
hooked it up for the FPs that currently accept one.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2873

Change-Id: Iaf93e379e405fbf745f5e0fd23b4daf017355966
Reviewed-on: https://skia-review.googlesource.com/2873
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
6 files changed