Add scanline decoding to SkCodec.

src/images/SkImageDecoder_libpng.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageDecoder.h"
 #include "SkImageEncoder.h"
 #include "SkColor.h"
@@ skipping 357 matching lines @@
         return kFailure;
     }
 
     /* Turn on interlace handling.  REQUIRED if you are not using
     *  png_read_image().  To see how to handle interlacing passes,
     *  see the png_read_row() method below:
     */
     const int number_passes = (interlaceType != PNG_INTERLACE_NONE) ?
                               png_set_interlace_handling(png_ptr) : 1;
 
+    if (number_passes > 1) {
+        // For simplified comparison, only do the ones that are not interlaced.
+        return kFailure;
+    }
+
     /* Optional call to gamma correct and add the background to the palette
     *  and update info structure.  REQUIRED if you are expecting libpng to
     *  update the palette for you (ie you selected such a transform above).
     */
     png_read_update_info(png_ptr, info_ptr);
 
     if ((kAlpha_8_SkColorType == colorType || kIndex_8_SkColorType == colorType) &&
             1 == sampleSize) {
         if (kAlpha_8_SkColorType == colorType) {
             // For an A8 bitmap, we assume there is an alpha for speed. It is
@@ skipping 888 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 SkImageEncoder* sk_libpng_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kPNG_Type == t) ? SkNEW(SkPNGImageEncoder) : NULL;
 }
 
 static SkImageDecoder_DecodeReg gDReg(sk_libpng_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_png);
 static SkImageEncoder_EncodeReg gEReg(sk_libpng_efactory);