Move optional.h to webrtc/api/

webrtc/audio/time_interval.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_AUDIO_TIME_INTERVAL_H_
 #define WEBRTC_AUDIO_TIME_INTERVAL_H_
 
 #include <stdint.h>
 
-#include "webrtc/rtc_base/optional.h"
+#include "webrtc/api/optional.h"
 
 namespace webrtc {
 
 // This class logs the first and last time its Extend() function is called.
 //
 // This class is not thread-safe; Extend() calls should only be made by a
 // single thread at a time, such as within a lock or destructor.
 //
 // Example usage:
 //   // let x < y < z < u < v
@@ skipping 29 matching lines @@
     Interval(int64_t first, int64_t last);
 
     int64_t first, last;
   };
   rtc::Optional<Interval> interval_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_AUDIO_TIME_INTERVAL_H_