tools/gn: Make it 'gn check' clean.

tools/gn/BUILD.gn

 # Copyright (c) 2013 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.
 
 defines = [ "GN_BUILD" ]
 
 static_library("gn_lib") {
   sources = [
     "action_target_generator.cc",
     "action_target_generator.h",
@@ skipping 194 matching lines @@
 }
 
 executable("gn") {
   sources = [
     "gn_main.cc",
   ]
 
   deps = [
     ":gn_lib",
     ":last_commit_position",
+    "//base",
   ]
 }
 
 test("gn_unittests") {
   sources = [
     "action_target_generator_unittest.cc",
     "builder_unittest.cc",
     "c_include_iterator_unittest.cc",
     "command_format_unittest.cc",
     "config_values_extractors_unittest.cc",
@@ skipping 50 matching lines @@
 }
 
 executable("generate_test_gn_data") {
   sources = [
     "generate_test_gn_data.cc",
   ]
   deps = [
     "//base",
   ]
 }