Update to current webrtc library

This is from the upstream library commit id
3326535126e435f1ba647885ce43a8f0f3d317eb, corresponding to Chromium
88.0.4290.1.

webrtc/modules/audio_processing/aec3/reverb_frequency_response.cc

@@ -0,0 +1,98 @@
+/*
+ *  Copyright (c) 2018 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 "modules/audio_processing/aec3/reverb_frequency_response.h"
+
+#include <stddef.h>
+
+#include <algorithm>
+#include <array>
+#include <numeric>
+
+#include "api/array_view.h"
+#include "modules/audio_processing/aec3/aec3_common.h"
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+
+namespace {
+
+// Computes the ratio of the energies between the direct path and the tail. The
+// energy is computed in the power spectrum domain discarding the DC
+// contributions.
+float AverageDecayWithinFilter(
+    rtc::ArrayView<const float> freq_resp_direct_path,
+    rtc::ArrayView<const float> freq_resp_tail) {
+  // Skipping the DC for the ratio computation
+  constexpr size_t kSkipBins = 1;
+  RTC_CHECK_EQ(freq_resp_direct_path.size(), freq_resp_tail.size());
+
+  float direct_path_energy =
+      std::accumulate(freq_resp_direct_path.begin() + kSkipBins,
+                      freq_resp_direct_path.end(), 0.f);
+
+  if (direct_path_energy == 0.f) {
+    return 0.f;
+  }
+
+  float tail_energy = std::accumulate(freq_resp_tail.begin() + kSkipBins,
+                                      freq_resp_tail.end(), 0.f);
+  return tail_energy / direct_path_energy;
+}
+
+}  // namespace
+
+ReverbFrequencyResponse::ReverbFrequencyResponse() {
+  tail_response_.fill(0.f);
+}
+ReverbFrequencyResponse::~ReverbFrequencyResponse() = default;
+
+void ReverbFrequencyResponse::Update(
+    const std::vector<std::array<float, kFftLengthBy2Plus1>>&
+        frequency_response,
+    int filter_delay_blocks,
+    const absl::optional<float>& linear_filter_quality,
+    bool stationary_block) {
+  if (stationary_block || !linear_filter_quality) {
+    return;
+  }
+
+  Update(frequency_response, filter_delay_blocks, *linear_filter_quality);
+}
+
+void ReverbFrequencyResponse::Update(
+    const std::vector<std::array<float, kFftLengthBy2Plus1>>&
+        frequency_response,
+    int filter_delay_blocks,
+    float linear_filter_quality) {
+  rtc::ArrayView<const float> freq_resp_tail(
+      frequency_response[frequency_response.size() - 1]);
+
+  rtc::ArrayView<const float> freq_resp_direct_path(
+      frequency_response[filter_delay_blocks]);
+
+  float average_decay =
+      AverageDecayWithinFilter(freq_resp_direct_path, freq_resp_tail);
+
+  const float smoothing = 0.2f * linear_filter_quality;
+  average_decay_ += smoothing * (average_decay - average_decay_);
+
+  for (size_t k = 0; k < kFftLengthBy2Plus1; ++k) {
+    tail_response_[k] = freq_resp_direct_path[k] * average_decay_;
+  }
+
+  for (size_t k = 1; k < kFftLengthBy2; ++k) {
+    const float avg_neighbour =
+        0.5f * (tail_response_[k - 1] + tail_response_[k + 1]);
+    tail_response_[k] = std::max(tail_response_[k], avg_neighbour);
+  }
+}
+
+}  // namespace webrtc