Create pdfium_unittests binary.

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.
 
 pdf_use_skia = false
 
 config("pdfium_config") {
   cflags = []
   include_dirs = [
     "third_party/freetype/include"
@@ skipping 773 matching lines @@
     "fpdfsdk/src/formfiller/FFL_ListBox.cpp",
     "fpdfsdk/src/formfiller/FFL_Notify.cpp",
     "fpdfsdk/src/formfiller/FFL_PushButton.cpp",
     "fpdfsdk/src/formfiller/FFL_RadioButton.cpp",
     "fpdfsdk/src/formfiller/FFL_TextField.cpp",
     "fpdfsdk/src/formfiller/FFL_Utils.cpp",
   ]
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ ":pdfium_config", "//build/config/compiler:no_chromium_code" ]
 }
+
+executable("pdfium_unittests") {
+  testonly = true
+  sources = [
+    "core/src/fxcrt/fx_basic_bstring_unittest.cpp",
+  ]
+  deps = [
+    ":pdfium",
+    "//base",
+    "//base/test:run_all_unittests",
+    "//testing/gtest",
+  ]
+}