Fix GN build

TBR=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1806683003 .
diff --git a/BUILD.gn b/BUILD.gn
index 4b5edbb..5058b5b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1491,6 +1491,7 @@
     "//testing/gtest",
     "//testing/gtest:gtest_main",
   ]
+  include_dirs = []
   if (pdf_enable_xfa) {
     sources += [
       "xfa/fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp",