switch xfermodes over to sk_sp

include/effects/SkArithmeticMode.h

Index: include/effects/SkArithmeticMode.h
diff --git a/include/effects/SkArithmeticMode.h b/include/effects/SkArithmeticMode.h
index 9e8df2e5cf7c26d5f2bbbca1aa81c80c458ae22a..b160dc7e9bf2544fcc68e2be66fae1adbdf06a1a 100644
--- a/include/effects/SkArithmeticMode.h
+++ b/include/effects/SkArithmeticMode.h
@@ -10,8 +10,7 @@
 
 #include "SkFlattenable.h"
 #include "SkScalar.h"
-
-class SkXfermode;
+#include "SkXfermode.h"
 
 class SK_API SkArithmeticMode {
 public:
@@ -22,9 +21,15 @@ public:
      *  k1=k3=k4=0, k2=1.0 results in returning the src
      *  k1=k2=k4=0, k3=1.0 results in returning the dst
      */
+    static sk_sp<SkXfermode> Make(SkScalar k1, SkScalar k2, SkScalar k3, SkScalar k4,
+                                  bool enforcePMColor = true);
+#ifdef SK_SUPPORT_LEGACY_XFERMODE_PTR
     static SkXfermode* Create(SkScalar k1, SkScalar k2,
                               SkScalar k3, SkScalar k4,
-                              bool enforcePMColor = true);
+                              bool enforcePMColor = true) {
+        return Make(k1, k2, k3, k4, enforcePMColor).release();
+    }
+#endif
 
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP();