Add more components unittests to the GN build.

components/login/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.
 
 component("login") {
   sources = [
     "base_screen_handler_utils.cc",
     "base_screen_handler_utils.h",
     "screens/screen_context.cc",
     "screens/screen_context.h",
   ]
 
   defines = [
     "LOGIN_IMPLEMENTATION"
   ]
 
   deps = [
     "//base",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = ["screens/screen_context_unittest.cc"]
 
   deps = [
     ":login",
+    "//base",
     "//testing/gtest",
   ]
 }