Move optional.h to webrtc/api/

webrtc/common_audio/smoothing_filter.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_COMMON_AUDIO_SMOOTHING_FILTER_H_
 #define WEBRTC_COMMON_AUDIO_SMOOTHING_FILTER_H_
 
+#include "webrtc/api/optional.h"
 #include "webrtc/rtc_base/constructormagic.h"
-#include "webrtc/rtc_base/optional.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 class SmoothingFilter {
  public:
   virtual ~SmoothingFilter() = default;
   virtual void AddSample(float sample) = 0;
   virtual rtc::Optional<float> GetAverage() = 0;
   virtual bool SetTimeConstantMs(int time_constant_ms) = 0;
@@ skipping 37 matching lines @@
   float alpha_;
   float state_;
   int64_t last_state_time_ms_;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(SmoothingFilterImpl);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_AUDIO_SMOOTHING_FILTER_H_