Merge to XFA: Add pdfium_unittests to BUILD.gn

Original at URL: https://codereview.chromium.org/840343005

TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/809883005
diff --git a/BUILD.gn b/BUILD.gn
index 0d3d693..c4e4580 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1540,3 +1540,19 @@
     "//v8:v8_libplatform",
   ]
 }
+
+test("pdfium_unittests") {
+  sources = [
+    "core/src/fxcrt/fx_basic_bstring_unittest.cpp",
+    "testing/fx_string_testhelpers.cpp",
+    "testing/fx_string_testhelpers.h",
+  ]
+  deps = [
+    "//testing/gtest",
+    "//testing/gtest:gtest_main",
+    ":pdfium"
+  ]
+  include_dirs = [ "." ]
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [ ":pdfium_config", "//build/config/compiler:no_chromium_code" ]
+}