add const to encodePixels pixel parameter

include/core/SkPixelSerializer.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPixelSerializer_DEFINED
 #define SkPixelSerializer_DEFINED
 
@@ skipping 14 matching lines @@
      *  false, serialize another version (e.g. the result of encodePixels).
      */
     bool useEncodedData(const void* data, size_t len) {
         return this->onUseEncodedData(data, len);
     }
 
     /**
      *  Call to get the client's version of encoding these pixels. If it
      *  returns NULL, serialize the raw pixels.
      */
-    SkData* encodePixels(const SkImageInfo& info, void* pixels, size_t rowBytes) {
+    SkData* encodePixels(const SkImageInfo& info, const void* pixels, size_t rowBytes) {
         return this->onEncodePixels(info, pixels, rowBytes);
     }
 
 protected:
     /**
      *  Return true if you want to serialize the encoded data, false if you want
      *  another version serialized (e.g. the result of encodePixels).
      */
     virtual bool onUseEncodedData(const void* data, size_t len) = 0;
 
     /**
      *  If you want to encode these pixels, return the encoded data as an SkData
      *  Return null if you want to serialize the raw pixels.
      */
-    virtual SkData* onEncodePixels(const SkImageInfo&, void* pixels, size_t rowBytes) = 0;
+    virtual SkData* onEncodePixels(const SkImageInfo&, const void* pixels, size_t rowBytes) = 0;
 };
 #endif // SkPixelSerializer_DEFINED