add const to encodePixels pixel parameter

include/core/SkPixelSerializer.h

Index: include/core/SkPixelSerializer.h
diff --git a/include/core/SkPixelSerializer.h b/include/core/SkPixelSerializer.h
index 8fc445c753adcc8538ad8717b23329f5195f3a4c..d089209909816b720fb710206b0a6e8005a38f57 100644
--- a/include/core/SkPixelSerializer.h
+++ b/include/core/SkPixelSerializer.h
@@ -32,7 +32,7 @@ public:
      *  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);
     }
 
@@ -47,6 +47,6 @@ protected:
      *  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