move SkDither.h to private, remove unused shadeSpan16

include/effects/SkPerlinNoiseShader.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPerlinNoiseShader_DEFINED
 #define SkPerlinNoiseShader_DEFINED
 
@@ skipping 62 matching lines @@
 
 
     size_t contextSize() const override;
 
     class PerlinNoiseShaderContext : public SkShader::Context {
     public:
         PerlinNoiseShaderContext(const SkPerlinNoiseShader& shader, const ContextRec&);
         virtual ~PerlinNoiseShaderContext();
 
         void shadeSpan(int x, int y, SkPMColor[], int count) override;
-        void shadeSpan16(int x, int y, uint16_t[], int count) override;
 
     private:
         SkPMColor shade(const SkPoint& point, StitchData& stitchData) const;
         SkScalar calculateTurbulenceValueForPoint(
             int channel,
             StitchData& stitchData, const SkPoint& point) const;
         SkScalar noise2D(int channel,
                          const StitchData& stitchData, const SkPoint& noiseVector) const;
 
         SkMatrix fMatrix;
@@ skipping 25 matching lines @@
     const SkScalar                  fBaseFrequencyY;
     const int                       fNumOctaves;
     const SkScalar                  fSeed;
     const SkISize                   fTileSize;
     const bool                      fStitchTiles;
 
     typedef SkShader INHERITED;
 };
 
 #endif