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/alignment_mixer.h

@@ -0,0 +1,58 @@
+/*
+ *  Copyright (c) 2019 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_ALIGNMENT_MIXER_H_
+#define MODULES_AUDIO_PROCESSING_AEC3_ALIGNMENT_MIXER_H_
+
+#include <vector>
+
+#include "api/array_view.h"
+#include "api/audio/echo_canceller3_config.h"
+#include "modules/audio_processing/aec3/aec3_common.h"
+
+namespace webrtc {
+
+// Performs channel conversion to mono for the purpose of providing a decent
+// mono input for the delay estimation. This is achieved by analyzing all
+// incoming channels and produce one single channel output.
+class AlignmentMixer {
+ public:
+  AlignmentMixer(size_t num_channels,
+                 const EchoCanceller3Config::Delay::AlignmentMixing& config);
+
+  AlignmentMixer(size_t num_channels,
+                 bool downmix,
+                 bool adaptive_selection,
+                 float excitation_limit,
+                 bool prefer_first_two_channels);
+
+  void ProduceOutput(rtc::ArrayView<const std::vector<float>> x,
+                     rtc::ArrayView<float, kBlockSize> y);
+
+  enum class MixingVariant { kDownmix, kAdaptive, kFixed };
+
+ private:
+  const size_t num_channels_;
+  const float one_by_num_channels_;
+  const float excitation_energy_threshold_;
+  const bool prefer_first_two_channels_;
+  const MixingVariant selection_variant_;
+  std::array<size_t, 2> strong_block_counters_;
+  std::vector<float> cumulative_energies_;
+  int selected_channel_ = 0;
+  size_t block_counter_ = 0;
+
+  void Downmix(const rtc::ArrayView<const std::vector<float>> x,
+               rtc::ArrayView<float, kBlockSize> y) const;
+  int SelectChannel(rtc::ArrayView<const std::vector<float>> x);
+};
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AEC3_ALIGNMENT_MIXER_H_