Make onPrepareDraws const

src/gpu/batches/GrDrawAtlasBatch.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 GrDrawAtlasBatch_DEFINED
 #define GrDrawAtlasBatch_DEFINED
 
@@ skipping 27 matching lines @@
         } else {
             color->setKnownFourComponents(fGeoData[0].fColor);
         }
         coverage->setKnownSingleComponent(0xff);
         overrides->fUsePLSDstRead = false;
     }
 
     SkSTArray<1, Geometry, true>* geoData() { return &fGeoData; }
 
 private:
-    void onPrepareDraws(Target*) override;
+    void onPrepareDraws(Target*) const override;
 
     void initBatchTracker(const GrXPOverridesForBatch&) override;
 
     GrDrawAtlasBatch(const Geometry& geometry, const SkMatrix& viewMatrix, int spriteCount,
                      const SkRSXform* xforms, const SkRect* rects, const SkColor* colors);
 
     GrColor color() const { return fColor; }
     bool colorIgnored() const { return fColorIgnored; }
     const SkMatrix& viewMatrix() const { return fViewMatrix; }
     bool hasColors() const { return fHasColors; }
     int quadCount() const { return fQuadCount; }
     bool coverageIgnored() const { return fCoverageIgnored; }
     
     bool onCombineIfPossible(GrBatch* t, const GrCaps&) override;
     SkSTArray<1, Geometry, true> fGeoData;
     
     SkMatrix fViewMatrix;
     GrColor  fColor;
     int      fQuadCount;
     bool     fColorIgnored;
     bool     fCoverageIgnored;
     bool     fHasColors;
 
     typedef GrVertexBatch INHERITED;
 };
 
 #endif