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

src/gpu/effects/GrDisableColorXP.cpp

Index: src/gpu/effects/GrDisableColorXP.cpp
diff --git a/src/gpu/effects/GrDisableColorXP.cpp b/src/gpu/effects/GrDisableColorXP.cpp
index 637f99baf111fc0fb7f87efaaa4a7a866580d470..d97589dcb66588059c2963f07309e9a680ad7c3f 100644
--- a/src/gpu/effects/GrDisableColorXP.cpp
+++ b/src/gpu/effects/GrDisableColorXP.cpp
@@ -100,7 +100,8 @@ GrDisableColorXPFactory::GrDisableColorXPFactory() {
 }
 
 GrXferProcessor*
-GrDisableColorXPFactory::onCreateXferProcessor(const GrProcOptInfo& colorPOI,
+GrDisableColorXPFactory::onCreateXferProcessor(const GrDrawTargetCaps& caps,
+                                               const GrProcOptInfo& colorPOI,
                                                const GrProcOptInfo& covPOI,
                                                const GrDeviceCoordTexture* dstCopy) const {
     return DisableColorXP::Create();