Check XpFactory equality in DrawState

include/gpu/effects/GrPorterDuffXferProcessor.h

Index: include/gpu/effects/GrPorterDuffXferProcessor.h
diff --git a/include/gpu/effects/GrPorterDuffXferProcessor.h b/include/gpu/effects/GrPorterDuffXferProcessor.h
index d1b30cc931dbad8262aa077a554f90e5fb275b26..9ff3bea2ed81bf9b5741c7084a0535157ed52835 100644
--- a/include/gpu/effects/GrPorterDuffXferProcessor.h
+++ b/include/gpu/effects/GrPorterDuffXferProcessor.h
@@ -68,8 +68,12 @@ public:
     bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const SK_OVERRIDE;
 
 private:
-    GrPorterDuffXPFactory(GrBlendCoeff src, GrBlendCoeff dst)
-        : fSrc(src), fDst(dst) {}
+    GrPorterDuffXPFactory(GrBlendCoeff src, GrBlendCoeff dst); 
+
+    bool onIsEqual(const GrXPFactory& xpfBase) const SK_OVERRIDE {
+        const GrPorterDuffXPFactory& xpf = xpfBase.cast<GrPorterDuffXPFactory>();
+        return (fSrc == xpf.fSrc && fDst == xpf.fDst);
+    }
 
     GrBlendCoeff fSrc;
     GrBlendCoeff fDst;