Move optional.h to webrtc/api/

webrtc/voice_engine/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 121 matching lines @@
   ]
   deps = [
     ":audio_level",
     ":file_player",
     ":file_recorder",
     "..:webrtc_common",
     "../api:array_view",
     "../api:audio_mixer_api",
     "../api:call_api",
     "../api:libjingle_peerconnection_api",
+    "../api:optional",
     "../api:transport_api",
     "../api/audio_codecs:audio_codecs_api",
     "../api/audio_codecs:builtin_audio_decoder_factory",
     "../api/audio_codecs:builtin_audio_encoder_factory",
     "../audio/utility:audio_frame_operations",
     "../call:rtp_interfaces",
     "../common_audio",
     "../logging:rtc_event_log_api",
     "../modules:module_api",
     "../modules/audio_coding:audio_format_conversion",
@@ skipping 153 matching lines @@
         ]
       }
 
       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" ]
       }
     }
   }
 }