switch xfermodes over to sk_sp

gm/vertices.cpp

Index: gm/vertices.cpp
diff --git a/gm/vertices.cpp b/gm/vertices.cpp
index 9c4ccc16bb33d04b3bffb4c790f73fd67188b0bf..978d9e69c514d2e7de0a38f0f037729435a82584 100644
--- a/gm/vertices.cpp
+++ b/gm/vertices.cpp
@@ -154,7 +154,7 @@ protected:
         canvas->translate(4, 4);
         int x = 0;
         for (size_t j = 0; j < SK_ARRAY_COUNT(modes); ++j) {
-            SkXfermode* xfer = SkXfermode::Create(modes[j]);
+            auto xfer = SkXfermode::Make(modes[j]);
             canvas->save();
             for (size_t i = 0; i < SK_ARRAY_COUNT(rec); ++i) {
                 paint.setShader(rec[i].fShader);
@@ -170,7 +170,6 @@ protected:
             }
             canvas->restore();
             canvas->translate(0, 40);
-            SkSafeUnref(xfer);
         }
     }