Revert[8] "replace SkXfermode obj with SkBlendMode enum in paints"

tools/viewer/sk_app/mac/RasterWindowContext_mac.cpp

Index: tools/viewer/sk_app/mac/RasterWindowContext_mac.cpp
diff --git a/tools/viewer/sk_app/mac/RasterWindowContext_mac.cpp b/tools/viewer/sk_app/mac/RasterWindowContext_mac.cpp
index 47f349b2eb8e1ba6234f384511c5f713a01a1a0f..fd2f2effb102c7ee19702050c099d838b43c5ca6 100644
--- a/tools/viewer/sk_app/mac/RasterWindowContext_mac.cpp
+++ b/tools/viewer/sk_app/mac/RasterWindowContext_mac.cpp
@@ -121,7 +121,7 @@ void RasterWindowContext_mac::onSwapBuffers() {
                        (fDisplayParams.fColorSpace != nullptr ||
                         kRGBA_F16_SkColorType == fDisplayParams.fColorType);
         SkPaint gammaPaint;
-        gammaPaint.setXfermodeMode(SkXfermode::kSrc_Mode);
+        gammaPaint.setBlendMode(SkBlendMode::kSrc);
         if (doGamma) {
             gammaPaint.setColorFilter(SkGammaColorFilter::Make(1.0f / 2.2f));
         }