Rename png_ functions conflicting with chrome.

samples/BUILD.gn

 # 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.
 
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build_overrides/v8.gni")
 import("../pdfium.gni")
 
 group("samples") {
   testonly = true
   deps = [
     ":pdfium_test",
     ":pdfium_diff",
   ]
 }
 
 config("pdfium_samples_config") {
   defines = [
     "PNG_PREFIX",
-    "PNGPREFIX_H",
     "PNG_USE_READ_MACROS",
   ]
   include_dirs = [ ".." ]
   if (pdf_enable_v8) {
-    defines += [ "PDF_ENABLE_V8", ]
+    defines += [ "PDF_ENABLE_V8" ]
   }
   if (pdf_enable_xfa) {
-    defines += [ "PDF_ENABLE_XFA", ]
+    defines += [ "PDF_ENABLE_XFA" ]
   }
 }
 
 executable("pdfium_test") {
   testonly = true
   sources = [
-    "pdfium_test.cc",
     "image_diff_png.cc",
     "image_diff_png.h",
+    "pdfium_test.cc",
   ]
   deps = [
     "//build/config/sanitizers:deps",
     "//third_party/pdfium:pdfium",
     "//third_party/pdfium:test_support",
 
     # Regardless of whether the library ships against system freetype,
     # always link this binary against the bundled one for consistency
     # of results across platforms.
     "//third_party/pdfium/third_party:fx_freetype",
@@ skipping 25 matching lines @@
   ]
   if (!pdf_enable_xfa) {
     deps += [ "../third_party:fx_lpng" ]
   }
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     ":pdfium_samples_config",
     "//build/config/compiler:no_chromium_code",
   ]
 }