Add pdf layer code for PDFium XFA module

pdf/pdf.gyp

Index: pdf/pdf.gyp
diff --git a/pdf/pdf.gyp b/pdf/pdf.gyp
index f1e8e3e658db0dbc95bdde88350f95f14c3d80b1..efcc4e3e903fcf268c926704a5c5c7a702b186d7 100644
--- a/pdf/pdf.gyp
+++ b/pdf/pdf.gyp
@@ -2,6 +2,7 @@
   'variables': {
     'chromium_code': 1,
     'pdf_engine%': 0,  # 0 PDFium
+    'pdf_use_xfa%': 0,
   },
   'target_defaults': {
     'cflags': [
@@ -69,6 +70,9 @@
         '../content/common/page_zoom.cc',
       ],
       'conditions': [
+        ['pdf_use_xfa==1', {
+          'defines': ['_PDF_USE_XFA_'],

[Lei Zhang, 2014/11/06 04:08:08]

Can we rename this to "PDF_USE_XFA" ? We don't put leading/trailing underscores
in any other #defines.

[Bo Xu, 2014/11/06 05:43:51]

Done.

+        }],
         ['pdf_engine==0', {
           'sources': [
             'pdfium/pdfium_assert_matching_enums.cc',