Make onPrepareDraws const

src/gpu/batches/GrAAHairLinePathRenderer.cpp

Index: src/gpu/batches/GrAAHairLinePathRenderer.cpp
diff --git a/src/gpu/batches/GrAAHairLinePathRenderer.cpp b/src/gpu/batches/GrAAHairLinePathRenderer.cpp
index d17ed09da9deb43872f2a50902065964d74ea0a7..6432dfd38a0cb2bbf4925e74babc1c8274d89840 100644
--- a/src/gpu/batches/GrAAHairLinePathRenderer.cpp
+++ b/src/gpu/batches/GrAAHairLinePathRenderer.cpp
@@ -712,7 +712,7 @@ private:
 
     SkSTArray<1, Geometry, true>* geoData() { return &fGeoData; }
 
-    void onPrepareDraws(Target*) override;
+    void onPrepareDraws(Target*) const override;
 
     typedef SkTArray<SkPoint, true> PtArray;
     typedef SkTArray<int, true> IntArray;
@@ -790,7 +790,7 @@ private:
     typedef GrVertexBatch INHERITED;
 };
 
-void AAHairlineBatch::onPrepareDraws(Target* target) {
+void AAHairlineBatch::onPrepareDraws(Target* target) const {
     // Setup the viewmatrix and localmatrix for the GrGeometryProcessor.
     SkMatrix invert;
     if (!this->viewMatrix().invert(&invert)) {