Add XP to handle the cases where we disable color write.

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 fab14c732a852d2a48d8995b13132dbd95441d36..fa93a083a8e3b8ca2bb8d72bc7bb714691ffb644 100644
--- a/include/gpu/effects/GrPorterDuffXferProcessor.h
+++ b/include/gpu/effects/GrPorterDuffXferProcessor.h
@@ -12,7 +12,6 @@
 #include "GrXferProcessor.h"
 #include "SkXfermode.h"
 
-class GrInvariantOutput;
 class GrProcOptInfo;
 
 class GrPorterDuffXferProcessor : public GrXferProcessor {
@@ -68,7 +67,6 @@ public:
 
     GrXferProcessor::OptFlags getOptimizations(const GrProcOptInfo& colorPOI,
                                                const GrProcOptInfo& coveragePOI,
-                                               bool colorWriteDisabled,
                                                bool doesStencilWrite,
                                                GrColor* overrideColor,
                                                const GrDrawTargetCaps& caps) SK_OVERRIDE;
@@ -96,7 +94,6 @@ private:
 
     GrXferProcessor::OptFlags internalGetOptimizations(const GrProcOptInfo& colorPOI,
                                                        const GrProcOptInfo& coveragePOI,
-                                                       bool colorWriteDisabled,
                                                        bool doesStencilWrite);
 
     void calcOutputTypes(GrXferProcessor::OptFlags blendOpts, const GrDrawTargetCaps& caps,
@@ -130,15 +127,17 @@ public:
 
     bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const SK_OVERRIDE;
 
-    bool canApplyCoverage(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
-                          bool colorWriteDisabled) const SK_OVERRIDE;
+    bool canApplyCoverage(const GrProcOptInfo& colorPOI,
+                          const GrProcOptInfo& coveragePOI) const SK_OVERRIDE;
 
     bool canTweakAlphaForCoverage() const SK_OVERRIDE;
 
     void getInvariantOutput(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
-                            bool colorWriteDisabled,
                             GrXPFactory::InvariantOutput*) const SK_OVERRIDE;
 
+    bool willReadDst(const GrProcOptInfo& colorPOI,
+                     const GrProcOptInfo& coveragePOI) const SK_OVERRIDE;
+
 private:
     GrPorterDuffXPFactory(GrBlendCoeff src, GrBlendCoeff dst);