Don't create a GXPFactory when blend is SrcOver

src/gpu/GrPipelineBuilder.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrPipelineBuilder_DEFINED
 #define GrPipelineBuilder_DEFINED
 
@@ skipping 132 matching lines @@
 
     ///////////////////////////////////////////////////////////////////////////
     /// @name Blending
     ////
 
     /**
      * Installs a GrXPFactory. This object controls how src color, fractional pixel coverage,
      * and the dst color are blended.
      */
     const GrXPFactory* setXPFactory(const GrXPFactory* xpFactory) {
-        fXPFactory.reset(SkRef(xpFactory));
+        fXPFactory.reset(SkSafeRef(xpFactory));
         return xpFactory;
     }
 
     /**
      * Sets a GrXPFactory that will ignore src color and perform a set operation between the draws
      * output coverage and the destination. This is useful to render coverage masks as CSG.
      */
     void setCoverageSetOpXPFactory(SkRegion::Op regionOp, bool invertCoverage = false) {
         fXPFactory.reset(GrCoverageSetOpXPFactory::Create(regionOp, invertCoverage));
     }
 
     /**
      * Sets a GrXPFactory that disables color writes to the destination. This is useful when
      * rendering to the stencil buffer.
      */
     void setDisableColorXPFactory() {
         fXPFactory.reset(GrDisableColorXPFactory::Create());
     }
 
     const GrXPFactory* getXPFactory() const {
-        if (!fXPFactory) {
-            fXPFactory.reset(GrPorterDuffXPFactory::Create(SkXfermode::kSrc_Mode));
-        }
-        return fXPFactory.get();
+        return fXPFactory;
     }
 
     /**
      * Checks whether the xp will need destination in a texture to correctly blend.
      */
     bool willXPNeedDstTexture(const GrCaps& caps, const GrProcOptInfo& colorPOI,
                               const GrProcOptInfo& coveragePOI) const;
 
     /// @}
 
@@ skipping 217 matching lines @@
     FragmentProcessorArray                  fCoverageFragmentProcessors;
     GrClip                                  fClip;
 
     mutable GrProcOptInfo fColorProcInfo;
     mutable GrProcOptInfo fCoverageProcInfo;
 
     friend class GrPipeline;
 };
 
 #endif