Use dst copies in porter duffer XP to correctly render certain blends.

include/gpu/GrXferProcessor.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 GrXferProcessor_DEFINED
 #define GrXferProcessor_DEFINED
 
@@ skipping 275 matching lines @@
     GrXPFactory() : fClassID(kIllegalXPFClassID) {}
 
     template <typename XPF_SUBCLASS> void initClassID() {
          static uint32_t kClassID = GenClassID();
          fClassID = kClassID;
     }
 
     uint32_t fClassID;
 
 private:
-    virtual GrXferProcessor* onCreateXferProcessor(const GrProcOptInfo& colorPOI,
+    virtual GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
+                                                   const GrProcOptInfo& colorPOI,
                                                    const GrProcOptInfo& coveragePOI,
                                                    const GrDeviceCoordTexture* dstCopy) const = 0;
     /**
      *  Returns true if the XP generated by this factory will explicitly read dst in the fragment
      *  shader.
      */
-    virtual bool willReadDstColor(const GrProcOptInfo& colorPOI,
+    virtual bool willReadDstColor(const GrDrawTargetCaps& caps,
+                                  const GrProcOptInfo& colorPOI,
                                   const GrProcOptInfo& coveragePOI) const = 0;
 
     virtual bool onIsEqual(const GrXPFactory&) const = 0;
 
     static uint32_t GenClassID() {
         // fCurrXPFactoryID has been initialized to kIllegalXPFactoryID. The
         // atomic inc returns the old value not the incremented value. So we add
         // 1 to the returned value.
         uint32_t id = static_cast<uint32_t>(sk_atomic_inc(&gCurrXPFClassID)) + 1;
         if (!id) {
             SkFAIL("This should never wrap as it should only be called once for each GrXPFactory "
                    "subclass.");
         }
         return id;
     }
 
     enum {
         kIllegalXPFClassID = 0,
     };
     static int32_t gCurrXPFClassID;
 
     typedef GrProgramElement INHERITED;
 };
 
 #endif