Don't create a GXPFactory when blend is SrcOver

src/gpu/effects/GrDisableColorXP.h

Index: src/gpu/effects/GrDisableColorXP.h
diff --git a/src/gpu/effects/GrDisableColorXP.h b/src/gpu/effects/GrDisableColorXP.h
index caa0eecec8cc4a2219230f9803a2dd555c521fa6..a79dd9b971745b17bf9f012e336a5649aa4318b5 100644
--- a/src/gpu/effects/GrDisableColorXP.h
+++ b/src/gpu/effects/GrDisableColorXP.h
@@ -17,10 +17,6 @@ class GrDisableColorXPFactory : public GrXPFactory {
 public:
     static GrXPFactory* Create() { return new GrDisableColorXPFactory; }
 
-    bool supportsRGBCoverage(GrColor knownColor, uint32_t knownColorFlags) const override {
-        return true;
-    }
-
     void getInvariantBlendedColor(const GrProcOptInfo& colorPOI,
                                   GrXPFactory::InvariantBlendedColor* blendedColor) const override {
         blendedColor->fKnownColorFlags = kNone_GrColorComponentFlags;