Implement fast, correct gamma conversion for color xforms

tests/ColorSpaceXformTest.cpp

Index: tests/ColorSpaceXformTest.cpp
diff --git a/tests/ColorSpaceXformTest.cpp b/tests/ColorSpaceXformTest.cpp
index 220509b9f6390c165ff2885cc6e867f19ceaa3dc..9d0315b24944aac24e0210b92d7d347438930997 100644
--- a/tests/ColorSpaceXformTest.cpp
+++ b/tests/ColorSpaceXformTest.cpp
@@ -35,7 +35,7 @@ static void test_xform(skiatest::Reporter* r, const sk_sp<SkGammas>& gammas) {
     // Create and perform xform
     std::unique_ptr<SkColorSpaceXform> xform(
             ColorSpaceXformTest::CreateDefaultXform(gammas, srcToDst, gammas));
-    xform->xform_RGBA_8888(dstPixels, srcPixels, width);
+    xform->xform_RGB1_8888(dstPixels, srcPixels, width);
 
     // Since the matrix is the identity, and the gamma curves match, the pixels
     // should be unchanged.