Move optional.h to webrtc/api/

webrtc/modules/audio_processing/aec3/render_delay_controller_metrics_unittest.cc

 /*
  *  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.
  */
 
 #include "webrtc/modules/audio_processing/aec3/render_delay_controller_metrics.h"
+#include "webrtc/api/optional.h"
 #include "webrtc/modules/audio_processing/aec3/aec3_common.h"
-#include "webrtc/rtc_base/optional.h"
 
 #include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 // Verify the general functionality of RenderDelayControllerMetrics.
 TEST(RenderDelayControllerMetrics, NormalUsage) {
   RenderDelayControllerMetrics metrics;
 
   for (int j = 0; j < 3; ++j) {
     for (int k = 0; k < kMetricsReportingIntervalBlocks - 1; ++k) {
       metrics.Update(rtc::Optional<size_t>(), 0);
       EXPECT_FALSE(metrics.MetricsReported());
     }
     metrics.Update(rtc::Optional<size_t>(), 0);
     EXPECT_TRUE(metrics.MetricsReported());
   }
 }
 
 }  // namespace webrtc