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

include/gpu/GrXferProcessor.h

Index: include/gpu/GrXferProcessor.h
diff --git a/include/gpu/GrXferProcessor.h b/include/gpu/GrXferProcessor.h
index b9adb66a1ca4260762ba873ca5a3b5eec372c27c..8cb5cb17698f84464acc8ee14d27c337636b1a5f 100644
--- a/include/gpu/GrXferProcessor.h
+++ b/include/gpu/GrXferProcessor.h
@@ -293,14 +293,16 @@ protected:
     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;