Add mixed samples support to XPs

include/gpu/effects/GrCoverageSetOpXP.h

Index: include/gpu/effects/GrCoverageSetOpXP.h
diff --git a/include/gpu/effects/GrCoverageSetOpXP.h b/include/gpu/effects/GrCoverageSetOpXP.h
index 6067b5eebb72cd9f07551e8cabe86d7a0cd2bce1..8511074cbd39cd66690c49dbb101e582fee64a69 100644
--- a/include/gpu/effects/GrCoverageSetOpXP.h
+++ b/include/gpu/effects/GrCoverageSetOpXP.h
@@ -37,11 +37,13 @@ private:
     GrXferProcessor* onCreateXferProcessor(const GrCaps& caps,
                                            const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
+                                           bool hasMixedSamples,
                                            const DstTexture*) const override;
 
     bool willReadDstColor(const GrCaps& /*caps*/,
                           const GrProcOptInfo& /*colorPOI*/,
-                          const GrProcOptInfo& /*coveragePOI*/) const override {
+                          const GrProcOptInfo& /*coveragePOI*/,
+                          bool /*hasMixedSamples*/) const override {
         return false;
     }