Improve GN header checker, make //ui pass.

ui/message_center/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/features.gni")
 import("//build/config/ui.gni")
 
 component("message_center") {
-  defines = [ "MESSAGE_CENTER_IMPLEMENTATION" ]
-
   deps = [
     "//base",
     "//base:i18n",
     "//base/third_party/dynamic_annotations",
     "//skia",
     "//ui/accessibility",
     "//ui/base",
     "//ui/events",
     "//ui/gfx",
     "//ui/gfx/geometry",
+    "//ui/native_theme",
     "//ui/resources",
     "//ui/strings",
+    "//url",
   ]
 
+  defines = [ "MESSAGE_CENTER_IMPLEMENTATION" ]
+
   if (enable_notifications) {
     sources = [
       "cocoa/notification_controller.h",
       "cocoa/notification_controller.mm",
       "cocoa/opaque_views.h",
       "cocoa/opaque_views.mm",
       "cocoa/popup_collection.h",
       "cocoa/popup_collection.mm",
       "cocoa/popup_controller.h",
       "cocoa/popup_controller.mm",
@@ skipping 117 matching lines @@
   testonly = true
   sources = [
     "fake_message_center.h",
     "fake_message_center.cc",
     "fake_message_center_tray_delegate.h",
     "fake_message_center_tray_delegate.cc",
     "fake_notifier_settings_provider.h",
     "fake_notifier_settings_provider.cc",
   ]
 
+  public_deps = [
+    ":message_center",
+  ]
+
   deps = [
-    ":message_center",
     "//base",
     "//base/test:test_support",
     "//skia",
     "//ui/gfx",
     "//ui/gfx/geometry",
   ]
 }
 
 test("message_center_unittests") {
   sources = [
@@ skipping 48 matching lines @@
       deps += [
         # Compositor is needed by message_center_view_unittest.cc and for the
         # fonts used by bounded_label_unittest.cc.
         "//ui/compositor",
         "//ui/views",
         "//ui/views:test_support",
       ]
     }
   }  # enable_notifications
 }