Move optional.h to webrtc/api/

webrtc/media/engine/payload_type_mapper.h

 /*
  *  Copyright (c) 2016 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_MEDIA_ENGINE_PAYLOAD_TYPE_MAPPER_H_
 #define WEBRTC_MEDIA_ENGINE_PAYLOAD_TYPE_MAPPER_H_
 
 #include <map>
 #include <set>
 
 #include "webrtc/api/audio_codecs/audio_format.h"
+#include "webrtc/api/optional.h"
 #include "webrtc/media/base/codec.h"
-#include "webrtc/rtc_base/optional.h"
 
 namespace cricket {
 
 webrtc::SdpAudioFormat AudioCodecToSdpAudioFormat(const AudioCodec& ac);
 
 class PayloadTypeMapper {
  public:
   PayloadTypeMapper();
   ~PayloadTypeMapper();
 
@@ skipping 17 matching lines @@
   };
 
   int next_unused_payload_type_;
   int max_payload_type_;
   std::map<webrtc::SdpAudioFormat, int, SdpAudioFormatOrdering> mappings_;
   std::set<int> used_payload_types_;
 };
 
 }  // namespace cricket
 #endif  // WEBRTC_MEDIA_ENGINE_PAYLOAD_TYPE_MAPPER_H_