Improve GN header checker, make //ui pass.

ui/web_dialogs/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("web_dialogs") {
   sources = [
     "web_dialog_delegate.cc",
     "web_dialog_delegate.h",
     "web_dialog_ui.cc",
     "web_dialog_ui.h",
     "web_dialog_web_contents_delegate.cc",
     "web_dialog_web_contents_delegate.h",
     "web_dialogs_export.h",
   ]
 
   defines = [ "WEB_DIALOGS_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//content/public/browser",
     "//content/public/common",
     "//skia",
     "//ui/base",
+    "//url",
   ]
 }
 
 static_library("test_support") {
   sources = [
     "test/test_web_contents_handler.cc",
     "test/test_web_contents_handler.h",
     "test/test_web_dialog_delegate.cc",
     "test/test_web_dialog_delegate.h",
   ]
 
+  public_deps = [
+    ":web_dialogs",
+  ]
   deps = [
-    ":web_dialogs",
     "//base",
     "//content/public/browser",
     "//skia",
+    "//url",
   ]
 }