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/ns/prior_signal_model.h

@@ -0,0 +1,32 @@
+/*
+ *  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_NS_PRIOR_SIGNAL_MODEL_H_
+#define MODULES_AUDIO_PROCESSING_NS_PRIOR_SIGNAL_MODEL_H_
+
+namespace webrtc {
+
+// Struct for storing the prior signal model parameters.
+struct PriorSignalModel {
+  explicit PriorSignalModel(float lrt_initial_value);
+  PriorSignalModel(const PriorSignalModel&) = delete;
+  PriorSignalModel& operator=(const PriorSignalModel&) = delete;
+
+  float lrt;
+  float flatness_threshold = .5f;
+  float template_diff_threshold = .5f;
+  float lrt_weighting = 1.f;
+  float flatness_weighting = 0.f;
+  float difference_weighting = 0.f;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_NS_PRIOR_SIGNAL_MODEL_H_