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/moving_average.h

@@ -0,0 +1,45 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_AEC3_MOVING_AVERAGE_H_
+#define MODULES_AUDIO_PROCESSING_AEC3_MOVING_AVERAGE_H_
+
+#include <stddef.h>
+
+#include <vector>
+
+#include "api/array_view.h"
+
+namespace webrtc {
+namespace aec3 {
+
+class MovingAverage {
+ public:
+  // Creates an instance of MovingAverage that accepts inputs of length num_elem
+  // and averages over mem_len inputs.
+  MovingAverage(size_t num_elem, size_t mem_len);
+  ~MovingAverage();
+
+  // Computes the average of input and mem_len-1 previous inputs and stores the
+  // result in output.
+  void Average(rtc::ArrayView<const float> input, rtc::ArrayView<float> output);
+
+ private:
+  const size_t num_elem_;
+  const size_t mem_len_;
+  const float scaling_;
+  std::vector<float> memory_;
+  size_t mem_index_;
+};
+
+}  // namespace aec3
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AEC3_MOVING_AVERAGE_H_