Add build configuration for experimental Windows GDI code.

pdfium.gyp

Index: pdfium.gyp
diff --git a/pdfium.gyp b/pdfium.gyp
index a99469157c4c389dff20b5cdc9aa0703d57458cc..0e71a3208398ae19fd02eb0e31ad79255bf3f6bf 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -8,6 +8,7 @@
     'pdf_use_skia%': 0,
     'pdf_enable_v8%': 1,
     'pdf_enable_xfa%': 0, # Set to 1 by standalone.gypi in a standalone build.
+    'pdf_use_win32_gdi%': 0,
     'variables': {
       'clang_use_chrome_plugins': 1,
     },
@@ -44,6 +45,9 @@
       ['pdf_enable_xfa==1', {
         'defines': ['PDF_ENABLE_XFA'],
       }],
+      ['pdf_use_win32_gdi==1', {
+        'defines': ['PDFIUM_PRINT_TEXT_WITH_GDI'],
+      }],
       ['OS=="linux"', {
         'conditions': [
           ['target_arch=="x64"', {