Added a perf test for the residual echo detector.

webrtc/modules/audio_processing/test/performance_timer.cc

Index: webrtc/modules/audio_processing/test/performance_timer.cc
diff --git a/webrtc/modules/audio_processing/test/performance_timer.cc b/webrtc/modules/audio_processing/test/performance_timer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c4fcc0a7123feece4689dbd0f2ec211c5ef50be2
--- /dev/null
+++ b/webrtc/modules/audio_processing/test/performance_timer.cc
@@ -0,0 +1,59 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/audio_processing/test/performance_timer.h"
+
+#include <math.h>
+
+#include <numeric>
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+namespace test {
+
+PerformanceTimer::PerformanceTimer(int num_frames_to_process)
+    : clock_(webrtc::Clock::GetRealTimeClock()) {
+  timestamps_us_.reserve(num_frames_to_process);
+}
+
+PerformanceTimer::~PerformanceTimer() = default;
+
+void PerformanceTimer::StartTimer() {
+  start_timestamp_us_ = rtc::Optional<int64_t>(clock_->TimeInMicroseconds());
+}
+
+void PerformanceTimer::StopTimer() {
+  RTC_DCHECK(start_timestamp_us_);
+  timestamps_us_.push_back(clock_->TimeInMicroseconds() - *start_timestamp_us_);
+}
+
+double PerformanceTimer::GetDurationAverage() const {
+  RTC_DCHECK(!timestamps_us_.empty());
+  return static_cast<double>(
+             std::accumulate(timestamps_us_.begin(), timestamps_us_.end(), 0)) /
+         timestamps_us_.size();
+}
+
+double PerformanceTimer::GetDurationStandardDeviation() const {
+  RTC_DCHECK(!timestamps_us_.empty());
+  double average_duration = GetDurationAverage();
+
+  double variance = std::accumulate(
+      timestamps_us_.begin(), timestamps_us_.end(), 0.0,
+      [average_duration](const double& a, const int64_t& b) {
+        return a + (b - average_duration) * (b - average_duration);
+      });
+
+  return sqrt(variance / timestamps_us_.size());
+}
+
+}  // namespace test
+}  // namespace webrtc