Improve GN header checker, make //ui pass.

ui/display/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.
 
 import("//build/config/ui.gni")
 
 component("display") {
   sources = [
     "chromeos/display_configurator.cc",
     "chromeos/display_configurator.h",
@@ skipping 46 matching lines @@
 
 component("test_util") {
   output_name = "display_test_util"
   sources = [
     "chromeos/test/test_display_snapshot.cc",
     "chromeos/test/test_display_snapshot.h",
   ]
 
   defines = [ "DISPLAY_IMPLEMENTATION" ]
 
+  public_deps = [
+    ":display",
+  ]
   deps = [
     "//base",
     "//ui/gfx",
     "//ui/gfx/geometry",
   ]
 
   if (is_chromeos) {
     deps += [ "//ui/display/types" ]
   }
 }
 
 test("display_unittests") {
   sources = [
     "chromeos/display_configurator_unittest.cc",
     "chromeos/x11/display_util_x11_unittest.cc",
     "chromeos/x11/native_display_event_dispatcher_x11_unittest.cc",
     "util/display_util_unittest.cc",
     "util/edid_parser_unittest.cc",
   ]
 
   deps = [
+    ":test_util",
+    "//base",
     "//base/test:run_all_unittests",
     "//testing/gtest",
     "//ui/display/util",
     "//ui/gfx/geometry",
   ]
 
   if (is_chromeos) {
     deps += [
       ":display",
-      ":test_util",
       "//ui/display/types",
     ]
   }
 }