Allow building of XFA branch without XFA

pdfium.gyp

Index: pdfium.gyp
diff --git a/pdfium.gyp b/pdfium.gyp
index b0ce2e47645343e9bafe9185fe0dc604e6c44a37..cbe6256802f1af44a96b2061b578722d34694475 100644
--- a/pdfium.gyp
+++ b/pdfium.gyp
@@ -1,6 +1,7 @@
 {
   'variables': {
     'pdf_use_skia%': 0,
+    'pdf_enable_xfa%': 1,
     'conditions': [
       ['OS=="linux"', {
         'bundle_freetype%': 0,
@@ -26,6 +27,9 @@
       ['pdf_use_skia==1', {
         'defines': ['_SKIA_SUPPORT_'],
       }],
+      ['pdf_enable_xfa==1', {
+        'defines': ['PDF_ENABLE_XFA'],
+      }],
       ['OS=="linux"', {
         'conditions': [
           ['target_arch=="x64"', {
@@ -818,8 +822,14 @@
         'testing/fx_string_testhelpers.h',
         'testing/fx_string_testhelpers.cpp',
         'third_party/base/nonstd_unique_ptr_unittest.cpp',
-        'xfa/src/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp',
-        'xfa/src/fxfa/src/parser/xfa_utils_imp_unittest.cpp',
+      ],
+      'conditions': [
+        ['pdf_enable_xfa==1', {
+          'sources': [
+            'xfa/src/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp',
+            'xfa/src/fxfa/src/parser/xfa_utils_imp_unittest.cpp',
+          ],
+        }],
       ],
     },
     {