Added a new echo likelihood stat that reports the maximum value from a previous time period.

webrtc/modules/audio_processing/echo_detector/likelihood_aggregator.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_ECHO_DETECTOR_LIKELIHOOD_AGGREGATOR_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_LIKELIHOOD_AGGREGATOR_H_
+
+#include <deque>
+#include <vector>
+
+namespace webrtc {
+
+// This class keeps a sliding window of past echo likelihood values, and can
+// calculate the maximum.
+class LikelihoodAggregator {
+ public:
+  explicit LikelihoodAggregator(size_t window_size_frames);
+  ~LikelihoodAggregator();
+
+  // Add a new likelihood to the buffer. This will automatically remove the
+  // oldest likelihood value from the buffer.
+  void Update(float value);
+  // Return the maximum likelihood value in the buffer.
+  float Max() const;
+  // Fill the buffer with zeros.
+  void Clear();
+
+ private:
+  // The most recent echo likelihood values are stored in a rotating buffer.
+  std::vector<float> recent_values_;
+  // Array indices of the maximum and possible future maxima.
+  std::deque<size_t> maximum_candidates_;

[the sun, 2017/01/13 13:55:28]

I think a priority_queue may serve you better - then you'd have 2*log2 behavior
in Update() instead of the current pushing/popping.

[ivoc, 2017/01/13 14:40:36]

That sounds like a good suggestion, but I rewrote this class to Per's
suggestion, which is a much cheaper algorithm (although it doesn't produce exact
results).

+  // Where to insert the next element in the rotating buffer.
+  size_t insertion_index_ = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_LIKELIHOOD_AGGREGATOR_H_