Move optional.h to webrtc/api/

webrtc/modules/audio_processing/aec3/mock/mock_echo_remover.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_MODULES_AUDIO_PROCESSING_AEC3_MOCK_MOCK_ECHO_REMOVER_H_
 #define WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_MOCK_MOCK_ECHO_REMOVER_H_
 
 #include <vector>
 
+#include "webrtc/api/optional.h"
 #include "webrtc/modules/audio_processing/aec3/echo_path_variability.h"
 #include "webrtc/modules/audio_processing/aec3/echo_remover.h"
 #include "webrtc/modules/audio_processing/aec3/render_buffer.h"
-#include "webrtc/rtc_base/optional.h"
 #include "webrtc/test/gmock.h"
 
 namespace webrtc {
 namespace test {
 
 class MockEchoRemover : public EchoRemover {
  public:
   virtual ~MockEchoRemover() = default;
 
   MOCK_METHOD5(ProcessCapture,
                void(const rtc::Optional<size_t>& echo_path_delay_samples,
                     const EchoPathVariability& echo_path_variability,
                     bool capture_signal_saturation,
                     const RenderBuffer& render_buffer,
                     std::vector<std::vector<float>>* capture));
 
   MOCK_METHOD1(UpdateEchoLeakageStatus, void(bool leakage_detected));
 };
 
 }  // namespace test
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_MOCK_MOCK_ECHO_REMOVER_H_