Add destination color space to AsFPArgs. Eliminates last XFORMTODO.

src/effects/gradients/SkLinearGradient.cpp

Index: src/effects/gradients/SkLinearGradient.cpp
diff --git a/src/effects/gradients/SkLinearGradient.cpp b/src/effects/gradients/SkLinearGradient.cpp
index f1a9eaf1e2f739fe7e7ff9abdabcd71c7b35cf47..cdac5c8f5f01b2486a328ea4c5d9c270510f8d2c 100644
--- a/src/effects/gradients/SkLinearGradient.cpp
+++ b/src/effects/gradients/SkLinearGradient.cpp
@@ -420,7 +420,8 @@ sk_sp<GrFragmentProcessor> GrLinearGradient::TestCreate(GrProcessorTestData* d)
     auto shader = SkGradientShader::MakeLinear(points, colors, stops, colorCount, tm);
     SkMatrix viewMatrix = GrTest::TestMatrix(d->fRandom);
     sk_sp<GrFragmentProcessor> fp = shader->asFragmentProcessor(SkShader::AsFPArgs(
-        d->fContext, &viewMatrix, NULL, kNone_SkFilterQuality, SkSourceGammaTreatment::kRespect));
+        d->fContext, &viewMatrix, NULL, kNone_SkFilterQuality, nullptr,
+        SkSourceGammaTreatment::kRespect));
     GrAlwaysAssert(fp);
     return fp;
 }