Only discard for XP dstCopies if we have a coverage value.

src/gpu/effects/GrDisableColorXP.cpp

Index: src/gpu/effects/GrDisableColorXP.cpp
diff --git a/src/gpu/effects/GrDisableColorXP.cpp b/src/gpu/effects/GrDisableColorXP.cpp
index 261100deb97ca91ab893e1a7469d4c1ff9e26f97..9b513f663eafe6bd390e19e0be7056486c91c4b4 100644
--- a/src/gpu/effects/GrDisableColorXP.cpp
+++ b/src/gpu/effects/GrDisableColorXP.cpp
@@ -29,17 +29,17 @@ public:
 
     bool hasSecondaryOutput() const override { return false; }
 
-    GrXferProcessor::OptFlags getOptimizations(const GrProcOptInfo& colorPOI,
-                                               const GrProcOptInfo& coveragePOI,
-                                               bool doesStencilWrite,
-                                               GrColor* color,
-                                               const GrDrawTargetCaps& caps) override {
-        return GrXferProcessor::kIgnoreColor_OptFlag | GrXferProcessor::kIgnoreCoverage_OptFlag;
-    }
-
 private:
     DisableColorXP();
 
+    GrXferProcessor::OptFlags onGetOptimizations(const GrProcOptInfo& colorPOI,
+                                                 const GrProcOptInfo& coveragePOI,
+                                                 bool doesStencilWrite,
+                                                 GrColor* color,
+                                                 const GrDrawTargetCaps& caps) override {
+        return GrXferProcessor::kIgnoreColor_OptFlag | GrXferProcessor::kIgnoreCoverage_OptFlag;
+    }
+
     void onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;
 
     void onGetBlendInfo(GrXferProcessor::BlendInfo* blendInfo) const override;