Adding png scanline decoding to kIndex8

src/codec/SkCodec_libgif.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec_libgif.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 325 matching lines @@
                     imageTop = 0;
                 }
 
                 // Create a color table to store colors the giflib colorMap
                 SkPMColor alternateColorPtr[256];
                 SkPMColor* colorTable;
                 SkColorType dstColorType = dstInfo.colorType();
                 if (kIndex_8_SkColorType == dstColorType) {
                     SkASSERT(NULL != inputColorPtr);
                     SkASSERT(NULL != inputColorCount);
-                    SkASSERT(256 == *inputColorCount);
                     colorTable = inputColorPtr;
                 } else {
                     colorTable = alternateColorPtr;
                 }
 
                 // Set up the color table
                 uint32_t colorCount = 0;
                 // Allocate maximum storage to deal with invalid indices safely
                 const uint32_t maxColors = 256;
                 ColorMapObject* colorMap = fGif->Image.ColorMap;
@@ skipping 205 matching lines @@
                 // giflib returns an error code if the record type is not known.
                 // We should catch this error immediately.
                 SkASSERT(false);
                 break;
         }
     } while (TERMINATE_RECORD_TYPE != recordType);
 
     return gif_error("Could not find any images to decode in gif file.\n",
             kInvalidInput);
 }