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/gm/texdata.cpp b/gm/texdata.cpp
index c269448..05441ac 100644
--- a/gm/texdata.cpp
+++ b/gm/texdata.cpp
@@ -87,7 +87,7 @@
         GrFixedClip clip(SkIRect::MakeWH(2*S, 2*S));
 
         GrPaint paint;
-        paint.setPorterDuffXPFactory(SkXfermode::kSrcOver_Mode);
+        paint.setPorterDuffXPFactory(SkBlendMode::kSrcOver);
 
         SkMatrix vm;
         if (i) {