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

gm/picture.cpp

Index: gm/picture.cpp
diff --git a/gm/picture.cpp b/gm/picture.cpp
index 1ea8adaa7601dd583403927eea2847638f146671..72d4159aa97b866a8747e6cc497b04777375f5a1 100644
--- a/gm/picture.cpp
+++ b/gm/picture.cpp
@@ -29,7 +29,7 @@ static sk_sp<SkPicture> make_picture() {
     canvas->drawPath(path, paint);
 
     paint.setColor(0x80FFFFFF);
-    paint.setXfermodeMode(SkXfermode::kPlus_Mode);
+    paint.setBlendMode(SkBlendMode::kPlus);
     canvas->drawRect(SkRect::MakeXYWH(25, 25, 50, 50), paint);
 
     return rec.finishRecordingAsPicture();