Improve stability of the echo detector complexity perf tests.

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.
  */
 
@@ skipping 12 matching lines @@
  public:
   explicit PerformanceTimer(int num_frames_to_process);
   ~PerformanceTimer();
 
   void StartTimer();
   void StopTimer();
 
   double GetDurationAverage() const;
   double GetDurationStandardDeviation() const;
 
+  // These methods are the same as those above, but they ignore the first
+  // |number_of_warmup_samples| measurements.
+  double GetDurationAverage(size_t number_of_warmup_samples) const;
+  double GetDurationStandardDeviation(size_t number_of_warmup_samples) const;
+
  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_