Introduce GrColorSpaceXform, for gamut conversion on textures

src/effects/gradients/SkGradientShader.cpp

Index: src/effects/gradients/SkGradientShader.cpp
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 52fbe81daf454925cefdf472c07b04a5ee81efb9..8492dd5ccad5f1ccebcc1df085d104199e612534 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -1129,7 +1129,7 @@ GrGradientEffect::GrGradientEffect(GrContext* ctx,
         if (-1 != fRow) {
             fYCoord = fAtlas->getYOffset(fRow) + SK_ScalarHalf * fAtlas->getNormalizedTexelHeight();
             fCoordTransform.reset(kCoordSet, matrix, fAtlas->getTexture(), params.filterMode());
-            fTextureAccess.reset(fAtlas->getTexture(), params);
+            fTextureAccess.reset(fAtlas->getTexture(), nullptr, params);
         } else {
             SkAutoTUnref<GrTexture> texture(
                 GrRefCachedBitmapTexture(ctx, bitmap, params, SkSourceGammaTreatment::kRespect));
@@ -1137,7 +1137,7 @@ GrGradientEffect::GrGradientEffect(GrContext* ctx,
                 return;
             }
             fCoordTransform.reset(kCoordSet, matrix, texture, params.filterMode());
-            fTextureAccess.reset(texture, params);
+            fTextureAccess.reset(texture, nullptr, params);
             fYCoord = SK_ScalarHalf;
         }
         this->addTextureAccess(&fTextureAccess);