Move optional.h to webrtc/api/

webrtc/modules/audio_processing/test/performance_timer.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_AUDIO_PROCESSING_TEST_PERFORMANCE_TIMER_H_
 #define WEBRTC_MODULES_AUDIO_PROCESSING_TEST_PERFORMANCE_TIMER_H_
 
 #include <vector>
 
-#include "webrtc/rtc_base/optional.h"
+#include "webrtc/api/optional.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 namespace test {
 
 class PerformanceTimer {
  public:
   explicit PerformanceTimer(int num_frames_to_process);
   ~PerformanceTimer();
 
@@ skipping 11 matching lines @@
  private:
   webrtc::Clock* clock_;
   rtc::Optional<int64_t> start_timestamp_us_;
   std::vector<int64_t> timestamps_us_;
 };
 
 }  // namespace test
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_PROCESSING_TEST_PERFORMANCE_TIMER_H_