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/samplecode/SampleAtlas.cpp b/samplecode/SampleAtlas.cpp
index 3daf312..f89b37d 100644
--- a/samplecode/SampleAtlas.cpp
+++ b/samplecode/SampleAtlas.cpp
@@ -21,7 +21,7 @@
 static void draw_atlas(SkCanvas* canvas, SkImage* atlas, const SkRSXform xform[],
                        const SkRect tex[], const SkColor colors[], int count, const SkRect* cull,
                        const SkPaint* paint) {
-    canvas->drawAtlas(atlas, xform, tex, colors, count, SkXfermode::kModulate_Mode, cull, paint);
+    canvas->drawAtlas(atlas, xform, tex, colors, count, SkBlendMode::kModulate, cull, paint);
 }
 
 static void draw_atlas_sim(SkCanvas* canvas, SkImage* atlas, const SkRSXform xform[],