Replace fWillReadFragmentPosition with a bitfield

src/gpu/effects/GrConvexPolyEffect.cpp

Index: src/gpu/effects/GrConvexPolyEffect.cpp
diff --git a/src/gpu/effects/GrConvexPolyEffect.cpp b/src/gpu/effects/GrConvexPolyEffect.cpp
index cf874cfa52604e1666ddecad3fec720d1063279a..287d7a2cbac5a08dd0c1adfecc6d0b53e0f394f3 100644
--- a/src/gpu/effects/GrConvexPolyEffect.cpp
+++ b/src/gpu/effects/GrConvexPolyEffect.cpp
@@ -32,7 +32,7 @@ private:
     AARectEffect(GrPrimitiveEdgeType edgeType, const SkRect& rect)
         : fRect(rect), fEdgeType(edgeType) {
         this->initClassID<AARectEffect>();
-        this->setWillReadFragmentPosition();
+        this->enableBuiltInState(kFragmentPosition_BuiltInState);
     }
 
     GrGLSLFragmentProcessor* onCreateGLSLInstance() const override;
@@ -321,7 +321,7 @@ GrConvexPolyEffect::GrConvexPolyEffect(GrPrimitiveEdgeType edgeType, int n, cons
     for (int i = 0; i < n; ++i) {
         fEdges[3 * i + 2] += SK_ScalarHalf;
     }
-    this->setWillReadFragmentPosition();
+    this->enableBuiltInState(kFragmentPosition_BuiltInState);
 }
 
 bool GrConvexPolyEffect::onIsEqual(const GrFragmentProcessor& other) const {