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

webrtc/modules/audio_processing/echo_detector/moving_max.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/echo_detector/moving_max.h"
+
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+namespace {
+
+// Parameter for controlling how fast the estimated maximum decays after the
+// previous maximum is no longer valid. With a value of 0.95, the maximum will
+// decay to 1% of its former value after 90 updates.

[hlundin-webrtc, 2017/01/13 15:27:47]

This might be too fast, but I'm not sure.

[ivoc, 2017/01/13 15:48:52]

Changed this back to 0.99 per offline discussion.

+constexpr float kDecayFactor = 0.95f;
+
+}  // namespace
+
+MovingMax::MovingMax(size_t window_size) : window_size_(window_size) {
+  RTC_DCHECK_GT(window_size, 0);
+}
+
+MovingMax::~MovingMax() {}
+
+void MovingMax::Update(float value) {
+  if (value > max_value_) {
+    max_value_ = value;
+    counter_ = 0;

[the sun, 2017/01/13 15:16:02]

return;

otherwise you're effectively resetting counter_ to 1 (line 39)

[ivoc, 2017/01/13 15:48:52]

I shuffled things around so a return is not needed. However, I did need to
update the check for the counter, since it's value is compared before being
incremented.

[the sun, 2017/01/13 21:23:25]

Much nicer, but I'm not sure I agree with the (window_size_ - 1)... (nit)

+  }
+  if (counter_ >= window_size_) {
+    max_value_ *= kDecayFactor;
+  } else {
+    ++counter_;
+  }
+}
+
+float MovingMax::max() const {
+  return max_value_;
+}
+
+void MovingMax::Clear() {
+  max_value_ = 0.f;
+  counter_ = 0;
+}
+
+}  // namespace webrtc