Create helper functions to use in computeInvariantOutput calls

src/gpu/effects/GrDashingEffect.cpp

Index: src/gpu/effects/GrDashingEffect.cpp
diff --git a/src/gpu/effects/GrDashingEffect.cpp b/src/gpu/effects/GrDashingEffect.cpp
index d7a2f402da06424cbeb076976b2e7eb53fc5999b..7e20809cecceba5941bc0014ade0410ccb7b2459 100644
--- a/src/gpu/effects/GrDashingEffect.cpp
+++ b/src/gpu/effects/GrDashingEffect.cpp
@@ -585,8 +585,7 @@ GrGeometryProcessor* DashingCircleEffect::Create(GrPrimitiveEdgeType edgeType, c
 DashingCircleEffect::~DashingCircleEffect() {}
 
 void DashingCircleEffect::onComputeInvariantOutput(InvariantOutput* inout) const {
-    inout->fValidFlags = 0;
-    inout->fIsSingleComponent = false;
+    inout->mulByUnknownAlpha();
 }
 
 const GrBackendGeometryProcessorFactory& DashingCircleEffect::getFactory() const {
@@ -809,8 +808,7 @@ GrGeometryProcessor* DashingLineEffect::Create(GrPrimitiveEdgeType edgeType,
 DashingLineEffect::~DashingLineEffect() {}
 
 void DashingLineEffect::onComputeInvariantOutput(InvariantOutput* inout) const {
-    inout->fValidFlags = 0;
-    inout->fIsSingleComponent = false;
+    inout->mulByUnknownAlpha();
 }
 
 const GrBackendGeometryProcessorFactory& DashingLineEffect::getFactory() const {