Make onPrepareDraws const

src/gpu/batches/GrTestBatch.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrTestBatch_DEFINED
 #define GrTestBatch_DEFINED
 
@@ skipping 42 matching lines @@
     GrTestBatch(uint32_t classID, const GrGeometryProcessor* gp, const SkRect& bounds)
         : INHERITED(classID) {
         fGeometryProcessor.reset(SkRef(gp));
 
         this->setBounds(bounds);
     }
 
     const GrGeometryProcessor* geometryProcessor() const { return fGeometryProcessor; }
 
 private:
-    void onPrepareDraws(Target* target) override {
+    void onPrepareDraws(Target* target) const override {
         target->initDraw(fGeometryProcessor, this->pipeline());
         this->generateGeometry(target);
     }
 
     virtual Geometry* geoData(int index) = 0;
     virtual const Geometry* geoData(int index) const = 0;
 
     bool onCombineIfPossible(GrBatch* t, const GrCaps&) override {
         return false;
     }
 
-    virtual void generateGeometry(Target*) = 0;
+    virtual void generateGeometry(Target*) const = 0;
 
     struct BatchTracker {
         GrColor fColor;
         bool fUsesLocalCoords;
         bool fColorIgnored;
         bool fCoverageIgnored;
     };
 
     SkAutoTUnref<const GrGeometryProcessor> fGeometryProcessor;
     BatchTracker fBatch;
 
     typedef GrVertexBatch INHERITED;
 };
 
 #endif