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

src/effects/SkArithmeticMode_gpu.cpp

Index: src/effects/SkArithmeticMode_gpu.cpp
diff --git a/src/effects/SkArithmeticMode_gpu.cpp b/src/effects/SkArithmeticMode_gpu.cpp
index 469f5b1adbd7a3c85493b92793c55bdd88f77e8a..e068c9dc37d5958f4ccea30420914291719f1ac7 100644
--- a/src/effects/SkArithmeticMode_gpu.cpp
+++ b/src/effects/SkArithmeticMode_gpu.cpp
@@ -304,11 +304,12 @@ GrArithmeticXPFactory::GrArithmeticXPFactory(float k1, float k2, float k3, float
 }
 
 GrXferProcessor*
-GrArithmeticXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
+GrArithmeticXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
+                                             const GrProcOptInfo& colorPOI,
                                              const GrProcOptInfo& coveragePOI,
                                              const GrDeviceCoordTexture* dstCopy) const {
     return ArithmeticXP::Create(fK1, fK2, fK3, fK4, fEnforcePMColor, dstCopy,
-                                this->willReadDstColor(colorPOI, coveragePOI));
+                                this->willReadDstColor(caps, colorPOI, coveragePOI));
 }