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

src/gpu/effects/GrDisableColorXP.h

Index: src/gpu/effects/GrDisableColorXP.h
diff --git a/src/gpu/effects/GrDisableColorXP.h b/src/gpu/effects/GrDisableColorXP.h
index fe60b595a0c7140796e31f522085e376e9d78ef3..00675884a96bbf7e684356d049ab2a3af781e3cb 100644
--- a/src/gpu/effects/GrDisableColorXP.h
+++ b/src/gpu/effects/GrDisableColorXP.h
@@ -39,11 +39,13 @@ public:
 private:
     GrDisableColorXPFactory();
 
-    GrXferProcessor* onCreateXferProcessor(const GrProcOptInfo& colorPOI,
+    GrXferProcessor* onCreateXferProcessor(const GrDrawTargetCaps& caps,
+                                           const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
                                            const GrDeviceCoordTexture* dstCopy) const SK_OVERRIDE;
 
-    bool willReadDstColor(const GrProcOptInfo& colorPOI,
+    bool willReadDstColor(const GrDrawTargetCaps& caps,
+                          const GrProcOptInfo& colorPOI,
                           const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
         return false;
     }