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/dropshadowimagefilter.cpp b/gm/dropshadowimagefilter.cpp
index 370b569..fff318e 100644
--- a/gm/dropshadowimagefilter.cpp
+++ b/gm/dropshadowimagefilter.cpp
@@ -87,7 +87,7 @@
         };
 
         sk_sp<SkColorFilter> cf(SkColorFilter::MakeModeFilter(SK_ColorMAGENTA,
-                                                              SkXfermode::kSrcIn_Mode));
+                                                              SkBlendMode::kSrcIn));
         sk_sp<SkImageFilter> cfif(SkColorFilterImageFilter::Make(std::move(cf), nullptr));
         SkImageFilter::CropRect cropRect(SkRect::Make(SkIRect::MakeXYWH(10, 10, 44, 44)),
                                          SkImageFilter::CropRect::kHasAll_CropEdge);