Move optional.h to webrtc/api/

webrtc/modules/audio_coding/neteq/neteq_decoder_enum.h

 /*
  *  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.
  */
 
 #ifndef WEBRTC_MODULES_AUDIO_CODING_NETEQ_NETEQ_DECODER_ENUM_H_
 #define WEBRTC_MODULES_AUDIO_CODING_NETEQ_NETEQ_DECODER_ENUM_H_
 
 #include "webrtc/api/audio_codecs/audio_format.h"
-#include "webrtc/rtc_base/optional.h"
+#include "webrtc/api/optional.h"
 
 namespace webrtc {
 
 enum class NetEqDecoder {
   kDecoderPCMu,
   kDecoderPCMa,
   kDecoderPCMu_2ch,
   kDecoderPCMa_2ch,
   kDecoderILBC,
   kDecoderISAC,
@@ skipping 21 matching lines @@
   kDecoderArbitrary,
   kDecoderOpus,
   kDecoderOpus_2ch,
 };
 
 rtc::Optional<SdpAudioFormat> NetEqDecoderToSdpAudioFormat(NetEqDecoder nd);
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_NETEQ_DECODER_ENUM_H_