Move optional.h to webrtc/api/

webrtc/modules/audio_device/BUILD.gn

 # Copyright (c) 2014 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")
 
@@ skipping 265 matching lines @@
     if (!is_android && !is_ios) {
       visibility = [ "..:modules_unittests" ]
     }
     sources = [
       "fine_audio_buffer_unittest.cc",
     ]
     deps = [
       ":audio_device",
       ":mock_audio_device",
       "../../api:array_view",
+      "../../api:optional",
       "../../rtc_base:rtc_base_approved",
       "../../system_wrappers:system_wrappers",
       "../../test:test_support",
       "../utility:utility",
       "//testing/gmock",
     ]
     if (is_linux || is_mac || is_win) {
       sources += [ "audio_device_unittest.cc" ]
     }
     if (is_android) {
@@ skipping 37 matching lines @@
       "android/java/src/org/webrtc/voiceengine/WebRtcAudioUtils.java",
     ]
     deps = [
       "../../rtc_base:base_java",
     ]
 
     # TODO(sakal): Fix build hooks crbug.com/webrtc/8148
     no_build_hooks = true
   }
 }