Adding png scanline decoding to kIndex8

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 e9bcd043b4e35922830b07628ae0c58114c1c206..31463317649ae9fec2fbee007943bfc0ca7d0a26 100644
--- a/src/codec/SkCodec_libpng.h
+++ b/src/codec/SkCodec_libpng.h
@@ -30,7 +30,8 @@ protected:
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
             override;
     SkEncodedFormat onGetEncodedFormat() const override { return kPNG_SkEncodedFormat; }
-    SkScanlineDecoder* onGetScanlineDecoder(const SkImageInfo& dstInfo) override;
+    SkScanlineDecoder* onGetScanlineDecoder(const SkImageInfo& dstInfo, const Options& options,
+                                            SkPMColor ctable[], int* ctableCount) override;
     bool onReallyHasAlpha() const override { return fReallyHasAlpha; }
 private:
     png_structp                 fPng_ptr;
@@ -49,7 +50,7 @@ private:
 
     // 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&, int* ctableCount);
+                              size_t rowBytes, const Options&, SkPMColor*, int* ctableCount);
     // Calls rewindIfNeeded, and returns true if the decoder can continue.
     bool handleRewind();
     bool decodePalette(bool premultiply, int bitDepth, int* ctableCount);