remove xfermode from public api

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4020

CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I19cd056f2af778f10e8c6c2b7b2735593b43dbac
Reviewed-on: https://skia-review.googlesource.com/4020
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/tests/SRGBMipMapTest.cpp b/tests/SRGBMipMapTest.cpp
index a7f846c..073f667 100644
--- a/tests/SRGBMipMapTest.cpp
+++ b/tests/SRGBMipMapTest.cpp
@@ -129,7 +129,7 @@
     SkRect rect = SkRect::MakeWH(SkIntToScalar(rtS), SkIntToScalar(rtS));
     GrNoClip noClip;
     GrPaint paint;
-    paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
+    paint.setPorterDuffXPFactory(SkBlendMode::kSrc);
     GrTextureParams mipMapParams(SkShader::kRepeat_TileMode, GrTextureParams::kMipMap_FilterMode);
     paint.addColorTextureProcessor(texture, nullptr, SkMatrix::MakeScale(0.5f), mipMapParams);