Don't create a GXPFactory when blend is SrcOver

src/gpu/GrPipelineBuilder.h

Index: src/gpu/GrPipelineBuilder.h
diff --git a/src/gpu/GrPipelineBuilder.h b/src/gpu/GrPipelineBuilder.h
index 010685b3e2a85dce11a8082aa741810da0a37319..bf0bed56c9cbd7d1a8a3dac84d1a31337526b960 100644
--- a/src/gpu/GrPipelineBuilder.h
+++ b/src/gpu/GrPipelineBuilder.h
@@ -150,7 +150,7 @@ public:
      * and the dst color are blended.
      */
     const GrXPFactory* setXPFactory(const GrXPFactory* xpFactory) {
-        fXPFactory.reset(SkRef(xpFactory));
+        fXPFactory.reset(SkSafeRef(xpFactory));
         return xpFactory;
     }
 
@@ -171,10 +171,7 @@ public:
     }
 
     const GrXPFactory* getXPFactory() const {
-        if (!fXPFactory) {
-            fXPFactory.reset(GrPorterDuffXPFactory::Create(SkXfermode::kSrc_Mode));
-        }
-        return fXPFactory.get();
+        return fXPFactory;
     }
 
     /**