Keep pdf_engine in sync with PDF_ENABLE_XFA.

pdf/BUILD.gn

 # Copyright 2014 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("//third_party/pdfium/pdfium.gni")
+
 pdf_engine = 0  # 0 PDFium
 
 static_library("pdf") {
   sources = [
     "chunk_stream.cc",
     "chunk_stream.h",
     "document_loader.cc",
     "document_loader.h",
     "draw_utils.cc",
     "draw_utils.h",
@@ skipping 24 matching lines @@
       "pdfium/pdfium_mem_buffer_file_read.h",
       "pdfium/pdfium_mem_buffer_file_write.cc",
       "pdfium/pdfium_mem_buffer_file_write.h",
       "pdfium/pdfium_page.cc",
       "pdfium/pdfium_page.h",
       "pdfium/pdfium_range.cc",
       "pdfium/pdfium_range.h",
     ]
   }
 
+  if (pdf_enable_xfa) {
+    defines = [ "PDF_ENABLE_XFA" ]
+  }
+
   deps = [
     "//base",
     "//components/ui/zoom",
     "//content/public/common",
     "//gin",
     "//net",
     "//ppapi/cpp:objects",
     "//ppapi/cpp/private:internal_module",
     "//third_party/pdfium",
   ]
 }