Swizzling, except for premultiplying, done using libpng transforms

src/codec/SkCodec_libpng.h

Index: src/codec/SkCodec_libpng.h
diff --git a/src/codec/SkCodec_libpng.h b/src/codec/SkCodec_libpng.h
index a105c3c5e35659d3ee4ca3398108db7aa1ab21b2..f124e04eb5fcd8dfebced9da8c0c53c3be5201cd 100644
--- a/src/codec/SkCodec_libpng.h
+++ b/src/codec/SkCodec_libpng.h
@@ -44,15 +44,21 @@ private:
     SkSwizzler::SrcConfig       fSrcConfig;
     int                         fNumberPasses;
     bool                        fReallyHasAlpha;
+    int                         fBitDepth;
 
-    SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop);
+    SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop, int);
     ~SkPngCodec();
 
+
     // Helper to set up swizzler and color table. Also calls png_read_update_info.
     Result initializeSwizzler(const SkImageInfo& requestedInfo, void* dst,
                               size_t rowBytes, const Options&, SkPMColor*, int* ctableCount);
-    // Calls rewindIfNeeded, and returns true if the decoder can continue.
-    bool handleRewind();
+
+    // Sets libpng to decode to the data format of requestedInfo
+    Result setDataFormat(const SkImageInfo& requestedInfo);
+
+    // Calls rewindIfNeeded and setDataFormat and returns true if the decoder can continue.
+    bool handleRewind(const SkImageInfo& requestedInfo);
     bool decodePalette(bool premultiply, int bitDepth, int* ctableCount);
     void finish();
     void destroyReadStruct();