headless: Replace headless::Maybe with base::Optional

headless/BUILD.gn

 # Copyright 2015 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("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 
 group("headless") {
   deps = [
@@ skipping 223 matching lines @@
     "public/headless_browser.h",
     "public/headless_devtools_client.h",
     "public/headless_devtools_host.h",
     "public/headless_devtools_target.h",
     "public/headless_export.h",
     "public/headless_web_contents.h",
     "public/internal/message_dispatcher.h",
     "public/internal/value_conversions.h",
     "public/util/error_reporter.cc",
     "public/util/error_reporter.h",
-    "public/util/maybe.h",
   ]
 
   deps = [
     ":gen_devtools_client_api",
     ":pak",
     "//base",
     "//components/devtools_http_handler",
     "//content/public/app:both",
     "//content/public/browser",
     "//content/public/child",
@@ skipping 16 matching lines @@
     ":client_api_generator_tests",
     ":headless_browsertests",
     ":headless_unittests",
   ]
 }
 
 test("headless_unittests") {
   sources = [
     "public/domains/types_unittest.cc",
     "public/util/error_reporter_unittest.cc",
-    "public/util/maybe_unittest.cc",
   ]
 
   deps = [
     ":headless_lib",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//testing/gtest",
   ]
 }
 
@@ skipping 42 matching lines @@
   sources = [
     "app/headless_shell.cc",
     "app/headless_shell_switches.cc",
     "app/headless_shell_switches.h",
   ]
 
   deps = [
     "//headless:headless_lib",
   ]
 }