switch xfermodes over to sk_sp

waiting on https://codereview.chromium.org/1835163002/

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1832223002

Review URL: https://codereview.chromium.org/1832223002
diff --git a/tools/debugger/SkOverdrawMode.cpp b/tools/debugger/SkOverdrawMode.cpp
index 3b695ec..7eee387 100644
--- a/tools/debugger/SkOverdrawMode.cpp
+++ b/tools/debugger/SkOverdrawMode.cpp
@@ -317,7 +317,7 @@
     return Create();
 }
 
-SkXfermode* SkOverdrawMode::Create() { return new SkOverdrawXfermode; }
+sk_sp<SkXfermode> SkOverdrawMode::Make() { return sk_make_sp<SkOverdrawXfermode>(); }
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkOverdrawMode)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkOverdrawXfermode)