SkPDF: use sk_ref_sp

src/pdf/SkPDFGraphicState.cpp

Index: src/pdf/SkPDFGraphicState.cpp
diff --git a/src/pdf/SkPDFGraphicState.cpp b/src/pdf/SkPDFGraphicState.cpp
index 19e9a36d05ca52520787a00e5dfa310b99e22f32..8fad7497c20097a15e450e8dcedaaf76f11d63fc 100644
--- a/src/pdf/SkPDFGraphicState.cpp
+++ b/src/pdf/SkPDFGraphicState.cpp
@@ -165,7 +165,7 @@ SkPDFDict* SkPDFGraphicState::GetSMaskGraphicState(SkPDFFormXObject* sMask,
     } else if (sMaskMode == kLuminosity_SMaskMode) {
         sMaskDict->insertName("S", "Luminosity");
     }
-    sMaskDict->insertObjRef("G", sk_sp<SkPDFFormXObject>(SkRef(sMask)));
+    sMaskDict->insertObjRef("G", sk_ref_sp(sMask));
     if (invert) {
         sMaskDict->insertObjRef("TR", make_invert_function());
     }