Rename png_ functions conflicting with chrome.

BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_config") {
   cflags = []
   include_dirs = [
     ".",
     "third_party/freetype/include",
     "third_party/freetype/include/freetype",
   ]
   defines = [
     "OPJ_STATIC",
     "PNG_PREFIX",
-    "PNGPREFIX_H",
     "PNG_USE_READ_MACROS",
     "V8_DEPRECATION_WARNINGS",
     "_CRT_SECURE_NO_WARNINGS",
   ]
 
   if (pdf_use_skia) {
     defines += [ "_SKIA_SUPPORT_" ]
   }
 
   if (pdf_enable_v8) {
@@ skipping 1470 matching lines @@
       "//v8:v8_libplatform",
     ]
     include_dirs += [
       "//v8",
       "//v8/include",
     ]
     configs += [ "//v8:external_startup_data" ]
   }
   configs += [ ":pdfium_config" ]
 }