Add build configuration for experimental Windows GDI code.

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_common_config") {
   cflags = []
@@ skipping 12 matching lines @@
     defines += [ "_SKIA_SUPPORT_" ]
   }
 
   if (pdf_enable_v8) {
     defines += [ "PDF_ENABLE_V8" ]
   }
 
   if (pdf_enable_xfa) {
     defines += [ "PDF_ENABLE_XFA" ]
   }
+
+  if (pdf_use_win32_gdi) {
+    defines += [ "PDFIUM_PRINT_TEXT_WITH_GDI" ]
+  }
 }
 
 config("pdfium_core_config") {
   cflags = []
   configs = [ ":pdfium_common_config" ]
   defines = [ "V8_DEPRECATION_WARNINGS" ]
   if (is_linux) {
     if (current_cpu == "x64") {
       defines += [ "_FX_CPU_=_FX_X64_" ]
       cflags += [ "-fPIC" ]
@@ skipping 1588 matching lines @@
 }
 
 if (pdf_is_standalone) {
   source_set("samples") {
     testonly = true
     deps = [
       "//samples",
     ]
   }
 }