change flattenable factory to return sk_sp

tools/debugger/SkOverdrawMode.cpp

Index: tools/debugger/SkOverdrawMode.cpp
diff --git a/tools/debugger/SkOverdrawMode.cpp b/tools/debugger/SkOverdrawMode.cpp
index 7eee387b091922108ddf3084ab78ada99bf96dbc..1e018babdbd40944b021aecd8e60747505b2c6dd 100644
--- a/tools/debugger/SkOverdrawMode.cpp
+++ b/tools/debugger/SkOverdrawMode.cpp
@@ -313,8 +313,8 @@ private:
     typedef SkXfermode INHERITED;
 };
 
-SkFlattenable* SkOverdrawXfermode::CreateProc(SkReadBuffer& buffer) {
-    return Create();
+sk_sp<SkFlattenable> SkOverdrawXfermode::CreateProc(SkReadBuffer& buffer) {
+    return sk_sp<SkFlattenable>(Create());
 }
 
 sk_sp<SkXfermode> SkOverdrawMode::Make() { return sk_make_sp<SkOverdrawXfermode>(); }