Move optional.h to webrtc/api/

webrtc/rtc_tools/network_tester/BUILD.gn

 # Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("../../webrtc.gni")
 import("//third_party/protobuf/proto_library.gni")
@@ skipping 23 matching lines @@
       "packet_sender.h",
       "test_controller.cc",
       "test_controller.h",
     ]
 
     defines = [ "WEBRTC_NETWORK_TESTER_PROTO" ]
 
     deps = [
       ":network_tester_config_proto",
       ":network_tester_packet_proto",
+      "../../api:optional",
       "../../p2p",
       "../../rtc_base:protobuf_utils",
       "../../rtc_base:rtc_base_approved",
       "../../rtc_base:rtc_task_queue",
       "../../rtc_base:sequenced_task_checker",
     ]
 
     if (!build_with_chromium && is_clang) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).
       suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
@@ skipping 114 matching lines @@
       ":network_tester",
       "../../system_wrappers:field_trial_default",
     ]
 
     suppressed_configs += [ "//build/config/android:hide_all_but_jni_onload" ]
     configs += [ "//build/config/android:hide_all_but_jni" ]
 
     output_extension = "so"
   }
 }