third_party/libpng: update to 1.2.54

TBR=darin@chromium.org
BUG=560291

Review URL: https://codereview.chromium.org/1467263003

Cr-Commit-Position: refs/heads/master@{#362298}
png_get_gAMA_fixed(png_structp png_ptr, png_infop info_ptr,
    png_fixed_point *int_file_gamma)
{
   png_debug1(1, "in %s retrieval function", "gAMA");

   if (png_ptr != NULL && info_ptr != NULL && (info_ptr->valid & PNG_INFO_gAMA)
      && int_file_gamma != NULL)
   {
      *int_file_gamma = info_ptr->int_gamma;
      return (PNG_INFO_gAMA);
   }
   return (0);
}

png_get_gAMA_fixed(png_structp png_ptr, png_infop info_ptr,
    png_fixed_point *int_file_gamma)
{
   png_debug1(1, "in %s retrieval function", "gAMA");

   if (png_ptr != NULL && info_ptr != NULL && (info_ptr->valid & PNG_INFO_gAMA)
      && int_file_gamma != NULL)
   {
      *int_file_gamma = info_ptr->int_gamma;
      return (PNG_INFO_gAMA);
   }
   return (0);
}
