switch xfermodes over to sk_sp

gm/xfermodes2.cpp

Index: gm/xfermodes2.cpp
diff --git a/gm/xfermodes2.cpp b/gm/xfermodes2.cpp
index 0956af66df453826be1bc63dd95f5cd08543d1ad..b0d6ca3def83b8e2e1484cf40081aa00ef7346b1 100644
--- a/gm/xfermodes2.cpp
+++ b/gm/xfermodes2.cpp
@@ -41,8 +41,6 @@ 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();
 
@@ -59,7 +57,7 @@ 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();