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

src/gpu/effects/GrCoverageSetOpXP.h

Index: src/gpu/effects/GrCoverageSetOpXP.h
diff --git a/src/gpu/effects/GrCoverageSetOpXP.h b/src/gpu/effects/GrCoverageSetOpXP.h
index e3ce07ca75b710931b84ec2721379e02366fc285..d526aeded9847f24734252a18114206b0f44f838 100644
--- a/src/gpu/effects/GrCoverageSetOpXP.h
+++ b/src/gpu/effects/GrCoverageSetOpXP.h
@@ -12,7 +12,6 @@
 #include "GrXferProcessor.h"
 #include "SkRegion.h"
 
-class GrInvariantOutput;
 class GrProcOptInfo;
 
 /**
@@ -38,7 +37,6 @@ public:
 
     GrXferProcessor::OptFlags getOptimizations(const GrProcOptInfo& colorPOI,
                                                const GrProcOptInfo& coveragePOI,
-                                               bool colorWriteDisabled,
                                                bool doesStencilWrite,
                                                GrColor* color,
                                                const GrDrawTargetCaps& caps) SK_OVERRIDE;
@@ -75,17 +73,19 @@ public:
         return true;
     }
 
-    bool canApplyCoverage(const GrProcOptInfo& colorPOI, const GrProcOptInfo& coveragePOI,
-                          bool colorWriteDisabled) const SK_OVERRIDE {
+    bool canApplyCoverage(const GrProcOptInfo& colorPOI,
+                          const GrProcOptInfo& coveragePOI) const SK_OVERRIDE {
         return true;
     }
 
     bool canTweakAlphaForCoverage() const SK_OVERRIDE { return false; }
 
     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:
     GrCoverageSetOpXPFactory(SkRegion::Op regionOp, bool invertCoverage);