Add pdf layer code for PDFium XFA module

pdf/BUILD.gn

Index: pdf/BUILD.gn
diff --git a/pdf/BUILD.gn b/pdf/BUILD.gn
index 5e1f165b1c3fef9dfb4d30147f679f9dd9143572..70591c131277aa955811758bac012893b2a5ceca 100644
--- a/pdf/BUILD.gn
+++ b/pdf/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 pdf_engine = 0  # 0 PDFium
+pdf_use_xfa = 0
 
 # TODO(GYP) need support for loadable modules
 shared_library("pdf") {
@@ -65,6 +66,10 @@ shared_library("pdf") {
     ]
   }
 
+  if(pdf_use_xfa == 1) {

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

nit: space after if

+    defines += [ "_PDF_USE_XFA_" ]

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

You need to start with:

defines = []

after sources = [ ... ]

and also change the "defines =" below to "defines +="

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

Done.

[Lei Zhang, 2014/11/06 19:15:29]

You need to write it like:

defines = []
if (condition1) {
  defines += [d1]
}
if (condition2) {
 ...
}

As is, "defines" isn't defined on non-Windows platforms to start, and defines +=
[ "PDF_USE_XFA" ] won't work.

+  }
+
   if (is_win) {
     defines = [ "COMPILE_CONTENT_STATICALLY" ]
     cflags = [ "/wd4267" ]  # TODO(jschuh) size_t to int truncations.