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/include/gpu/effects/GrCustomXfermode.h b/include/gpu/effects/GrCustomXfermode.h
index 3bd3214..8632093 100644
--- a/include/gpu/effects/GrCustomXfermode.h
+++ b/include/gpu/effects/GrCustomXfermode.h
@@ -17,8 +17,8 @@
  * coefficients.
  */
 namespace GrCustomXfermode {
-    bool IsSupportedMode(SkXfermode::Mode mode);
-    sk_sp<GrXPFactory> MakeXPFactory(SkXfermode::Mode mode);
+    bool IsSupportedMode(SkBlendMode mode);
+    sk_sp<GrXPFactory> MakeXPFactory(SkBlendMode mode);
 };
 
 #endif