Don't ref/unref the static src-over xp

include/gpu/effects/GrPorterDuffXferProcessor.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrPorterDuffXferProcessor_DEFINED
 #define GrPorterDuffXferProcessor_DEFINED
 
 #include "GrTypes.h"
 #include "GrXferProcessor.h"
 #include "SkXfermode.h"
 
 class GrProcOptInfo;
 
 class GrPorterDuffXPFactory : public GrXPFactory {
 public:
     static GrXPFactory* Create(SkXfermode::Mode mode); 
 
     void getInvariantBlendedColor(const GrProcOptInfo& colorPOI,
                                   GrXPFactory::InvariantBlendedColor*) const override;
 
+
+    /** Because src-over is so common we special case it for performance reasons. If this returns
+        null then the SimpleSrcOverXP() below should be used. */
     static GrXferProcessor* CreateSrcOverXferProcessor(const GrCaps& caps,
                                                        const GrPipelineOptimizations& optimizations,
                                                        bool hasMixedSamples,
                                                        const GrXferProcessor::DstTexture*);
+    /** This XP implements non-LCD src-over using hw blend with no optimizations. It is returned
+        by reference because it is global and its ref-cnting methods are not thread safe. */
+    static const GrXferProcessor& SimpleSrcOverXP();
 
     static inline void SrcOverInvariantBlendedColor(
                                                 GrColor inputColor,
                                                 GrColorComponentFlags validColorFlags,
                                                 bool isOpaque,
                                                 GrXPFactory::InvariantBlendedColor* blendedColor) {
         if (!isOpaque) {
             blendedColor->fWillBlendWithDst = true;
             blendedColor->fKnownColorFlags = kNone_GrColorComponentFlags;
             return;
@@ skipping 28 matching lines @@
     GR_DECLARE_XP_FACTORY_TEST;
     static void TestGetXPOutputTypes(const GrXferProcessor*, int* outPrimary, int* outSecondary);
 
     SkXfermode::Mode fXfermode;
 
     friend class GrPorterDuffTest; // for TestGetXPOutputTypes()
     typedef GrXPFactory INHERITED;
 };
 
 #endif