Add xdisplaycheck back until //build dependency is removed

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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 361 matching lines @@
   }
 
   if (use_ozone) {
     deps += [
       "//ui/ozone",
       "//ui/ozone:ozone_unittests",
       "//ui/ozone/gl:ozone_gl_unittests",
     ]
   }
 
+  if (use_x11 || ozone_platform_x11) {
+    deps += [ "//tools/xdisplaycheck" ]
+  }
+
   if (enable_configuration_policy) {
     deps += [ "//components/policy:policy_templates" ]
   }
 
   if (v8_use_external_startup_data) {
     deps += [ "//gin:gin_v8_snapshot_fingerprint" ]
   }
 
   if (is_win) {
     deps += [
@@ skipping 705 matching lines @@
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }