Enabling ico decoding with use of png and bmp decoders

src/codec/SkCodec_libpng.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_libpng.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 170 matching lines @@
         *colorPtr = colorPtr[-1];
     }
 
     return SkNEW_ARGS(SkColorTable, (colorStorage, colorCount));
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // Creation
 ///////////////////////////////////////////////////////////////////////////////
 
-#define PNG_BYTES_TO_CHECK 4
-
 bool SkPngCodec::IsPng(SkStream* stream) {
     char buf[PNG_BYTES_TO_CHECK];
     if (stream->read(buf, PNG_BYTES_TO_CHECK) != PNG_BYTES_TO_CHECK) {
         return false;
     }
     if (png_sig_cmp((png_bytep) buf, (png_size_t)0, PNG_BYTES_TO_CHECK)) {
         return false;
     }
     return true;
 }
@@ skipping 277 matching lines @@
 
     // FIXME: do we need substituteTranspColor?
 
     if (reallyHasAlpha && requestedInfo.alphaType() != kOpaque_SkAlphaType) {
         // FIXME: We want to alert the caller. Is this the right way?
         SkImageInfo* modInfo = const_cast<SkImageInfo*>(&requestedInfo);
         *modInfo = requestedInfo.makeAlphaType(kOpaque_SkAlphaType);
     }
     return kSuccess;
 }