Create helper functions to use in computeInvariantOutput calls

src/gpu/effects/GrOvalEffect.cpp

Index: src/gpu/effects/GrOvalEffect.cpp
diff --git a/src/gpu/effects/GrOvalEffect.cpp b/src/gpu/effects/GrOvalEffect.cpp
index c4e272a6bb2eb9dca2e349621701786c336bf60e..3d8f207b9f74b9818f5c8f514f4b5cc2caf9cd2a 100644
--- a/src/gpu/effects/GrOvalEffect.cpp
+++ b/src/gpu/effects/GrOvalEffect.cpp
@@ -57,8 +57,7 @@ GrFragmentProcessor* CircleEffect::Create(GrPrimitiveEdgeType edgeType, const Sk
 }
 
 void CircleEffect::onComputeInvariantOutput(InvariantOutput* inout) const {
-    inout->fValidFlags = 0;
-    inout->fIsSingleComponent = false;
+    inout->mulByUnknownAlpha();
 }
 
 const GrBackendFragmentProcessorFactory& CircleEffect::getFactory() const {
@@ -232,8 +231,7 @@ GrFragmentProcessor* EllipseEffect::Create(GrPrimitiveEdgeType edgeType,
 }
 
 void EllipseEffect::onComputeInvariantOutput(InvariantOutput* inout) const {
-    inout->fValidFlags = 0;
-    inout->fIsSingleComponent = false;
+    inout->mulByUnknownAlpha();
 }
 
 const GrBackendFragmentProcessorFactory& EllipseEffect::getFactory() const {