Rename png_ functions conflicting with chrome.

third_party/third_party.gyp

 # Copyright 2014 PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'pdf_enable_xfa%': 0,  # Set to 1 by standalone.gypi in standalone builds.
   },
   'target_defaults': {
     'defines': [
       'OPJ_STATIC',
       'PNG_PREFIX',
-      'PNGPREFIX_H',
       'PNG_USE_READ_MACROS',
       '_CRT_SECURE_NO_WARNINGS',
     ],
     'include_dirs': [
       # This is implicit in GN.
       '<(DEPTH)',
       '..',
     ],
     'msvs_disabled_warnings': [
       4005, 4018, 4146, 4333, 4345, 4267
@@ skipping 249 matching lines @@
         'libpng16/png.c',
         'libpng16/png.h',
         'libpng16/pngconf.h',
         'libpng16/pngdebug.h',
         'libpng16/pngerror.c',
         'libpng16/pngget.c',
         'libpng16/pnginfo.h',
         'libpng16/pnglibconf.h',
         'libpng16/pngmem.c',
         'libpng16/pngpread.c',
+        'libpng16/pngprefix.h',
         'libpng16/pngpriv.h',
         'libpng16/pngread.c',
         'libpng16/pngrio.c',
         'libpng16/pngrtran.c',
         'libpng16/pngrutil.c',
         'libpng16/pngset.c',
         'libpng16/pngstruct.h',
         'libpng16/pngtrans.c',
         'libpng16/pngwio.c',
         'libpng16/pngwrite.c',
@@ skipping 88 matching lines @@
             'libtiff/tif_version.c',
             'libtiff/tif_warning.c',
             'libtiff/tif_write.c',
             'libtiff/tif_zip.c',
           ],
         },
       ],
     }],
   ],
 }