added support for PLS path rendering

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 097a890d569c1f72cd80cbfe550da903d04ecb57..0b37dc113e2b0e23919f962af7f15abed4f7eba1 100644
--- a/include/gpu/effects/GrCoverageSetOpXP.h
+++ b/include/gpu/effects/GrCoverageSetOpXP.h
@@ -36,9 +36,7 @@ private:
 
     bool willReadDstColor(const GrCaps& /*caps*/,
                           const GrPipelineOptimizations& /*optimizations*/,
-                          bool /*hasMixedSamples*/) const override {
-        return false;
-    }
+                          bool /*hasMixedSamples*/) const override;
 
     bool onIsEqual(const GrXPFactory& xpfBase) const override {
         const GrCoverageSetOpXPFactory& xpf = xpfBase.cast<GrCoverageSetOpXPFactory>();