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>
diff --git a/src/gpu/effects/GrSimpleTextureEffect.cpp b/src/gpu/effects/GrSimpleTextureEffect.cpp
index 6eb15e0..b05ac83 100644
--- a/src/gpu/effects/GrSimpleTextureEffect.cpp
+++ b/src/gpu/effects/GrSimpleTextureEffect.cpp
@@ -91,5 +91,6 @@
     GrCoordSet coordSet = kCoordSets[d->fRandom->nextULessThan(SK_ARRAY_COUNT(kCoordSets))];
 
     const SkMatrix& matrix = GrTest::TestMatrix(d->fRandom);
-    return GrSimpleTextureEffect::Make(d->fTextures[texIdx], nullptr, matrix, coordSet);
+    auto colorSpaceXform = GrTest::TestColorXform(d->fRandom);
+    return GrSimpleTextureEffect::Make(d->fTextures[texIdx], colorSpaceXform, matrix, coordSet);
 }