Create helper functions to use in computeInvariantOutput calls

src/gpu/effects/GrSingleTextureEffect.h

Index: src/gpu/effects/GrSingleTextureEffect.h
diff --git a/src/gpu/effects/GrSingleTextureEffect.h b/src/gpu/effects/GrSingleTextureEffect.h
index cba322eab4e32256703e10d9b01a797e0fe5e1cf..899755c4df99d8c385da0f02568dfe0e3e601e34 100644
--- a/src/gpu/effects/GrSingleTextureEffect.h
+++ b/src/gpu/effects/GrSingleTextureEffect.h
@@ -49,10 +49,10 @@ protected:
      * texture.
      */
     void updateInvariantOutputForModulation(InvariantOutput* inout) const {
-        if (inout->isOpaque() && GrPixelConfigIsOpaque(this->texture(0)->config())) {
-            inout->fValidFlags = kA_GrColorComponentFlag;
+        if (GrPixelConfigIsOpaque(this->texture(0)->config())) {
+            inout->mulByUnknownOpaqueColor();
         } else {
-            inout->fValidFlags = 0;
+            inout->mulByUnknownColor();
         }
     }