Move optional.h to webrtc/api/

webrtc/modules/video_coding/utility/moving_average.h

 /*
  *  Copyright (c) 2015 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_UTILITY_MOVING_AVERAGE_H_
 #define WEBRTC_MODULES_VIDEO_CODING_UTILITY_MOVING_AVERAGE_H_
 
 #include <vector>
 
-#include "webrtc/rtc_base/optional.h"
+#include "webrtc/api/optional.h"
 
 namespace webrtc {
 class MovingAverage {
  public:
   explicit MovingAverage(size_t s);
   void AddSample(int sample);
   rtc::Optional<int> GetAverage() const;
   rtc::Optional<int> GetAverage(size_t num_samples) const;
   void Reset();
   size_t size() const;
 
  private:
   size_t count_ = 0;
   int sum_ = 0;
   std::vector<int> sum_history_;
 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_UTILITY_MOVING_AVERAGE_H_