Move optional.h to webrtc/api/

webrtc/modules/video_coding/sequence_number_util.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_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_
 #define WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_
 
 #include <limits>
 #include <type_traits>
 
+#include "webrtc/api/optional.h"
 #include "webrtc/rtc_base/mod_ops.h"
-#include "webrtc/rtc_base/optional.h"
 #include "webrtc/rtc_base/safe_compare.h"
 
 namespace webrtc {
 
 // Test if the sequence number |a| is ahead or at sequence number |b|.
 //
 // If |M| is an even number and the two sequence numbers are at max distance
 // from each other, then the sequence number with the highest value is
 // considered to be ahead.
 template <typename T, T M>
@@ skipping 90 matching lines @@
   }
 
  private:
   uint64_t last_unwrapped_;
   rtc::Optional<T> last_value_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_SEQUENCE_NUMBER_UTIL_H_