switch xfermodes over to sk_sp

gm/xfermodes2.cpp

Index: gm/xfermodes2.cpp
diff --git a/gm/xfermodes2.cpp b/gm/xfermodes2.cpp
index 397f4e1e2963a3f1cc3464af8911fff992bfea6a..61b69684789d4a89a6cc4ba7eae1f0083a2eebe4 100644
--- a/gm/xfermodes2.cpp
+++ b/gm/xfermodes2.cpp
@@ -42,8 +42,6 @@ protected:
         SkScalar x = 0, y = 0;
         for (size_t m = 0; m <= SkXfermode::kLastMode; m++) {
             SkXfermode::Mode mode = static_cast<SkXfermode::Mode>(m);
-            SkXfermode* xm = SkXfermode::Create(mode);
-            SkAutoUnref aur(xm);
 
             canvas->save();
 
@@ -60,7 +58,7 @@ protected:
             p.setShader(fDst);
             canvas->drawRect(r, p);
             p.setShader(fSrc);
-            p.setXfermode(xm);
+            p.setXfermode(SkXfermode::Make(mode));
             canvas->drawRect(r, p);
 
             canvas->restore();