Add scanline decoding to SkCodec.

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 debb14b882b8914d96011c1822afc0bcc7a9e600..fa7b39d82fdb497527a47b2d0d6a4fe2abbabf1b 100644
--- a/src/codec/SkCodec_libpng.h
+++ b/src/codec/SkCodec_libpng.h
@@ -6,15 +6,17 @@
  */
 
 #include "SkCodec.h"
+#include "SkColorTable.h"
 #include "SkEncodedFormat.h"
 #include "SkImageInfo.h"
+#include "SkRefCnt.h"
+#include "SkSwizzler.h"
 
 extern "C" {
-    // FIXME: I'd like to force all platforms to use the same decoder, but this
-    // means an extra dependency on Mac/Win.
     #include "png.h"
 }
 
+class SkScanlineDecoder;
 class SkStream;
 
 class SkPngCodec : public SkCodec {
@@ -26,12 +28,30 @@ protected:
     Result onGetPixels(const SkImageInfo&, void*, size_t, const Options&, SkPMColor*, int*)
             SK_OVERRIDE;
     SkEncodedFormat onGetEncodedFormat() const SK_OVERRIDE { return kPNG_SkEncodedFormat; }
+    SkScanlineDecoder* onGetScanlineDecoder(const SkImageInfo& dstInfo) SK_OVERRIDE;
+    bool onReallyHasAlpha() const SK_OVERRIDE { return fReallyHasAlpha; }
 private:
-    png_structp             fPng_ptr;
-    png_infop               fInfo_ptr;
+    png_structp                 fPng_ptr;
+    png_infop                   fInfo_ptr;
+
+    // These are stored here so they can be used both by normal decoding and scanline decoding.
+    SkAutoTUnref<SkColorTable>  fColorTable;    // May be unpremul.
+    SkAutoTDelete<SkSwizzler>   fSwizzler;
+
+    SkSwizzler::SrcConfig       fSrcConfig;
+    int                         fNumberPasses;
+    bool                        fReallyHasAlpha;
 
     SkPngCodec(const SkImageInfo&, SkStream*, png_structp, png_infop);
     ~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&);
+    bool decodePalette(bool premultiply);
+    void finish();
+
+    friend class SkPngScanlineDecoder;
+
     typedef SkCodec INHERITED;
 };