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/agc2/compute_interpolated_gain_curve.h

@@ -0,0 +1,48 @@
+/*
+ *  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_AGC2_COMPUTE_INTERPOLATED_GAIN_CURVE_H_
+#define MODULES_AUDIO_PROCESSING_AGC2_COMPUTE_INTERPOLATED_GAIN_CURVE_H_
+
+#include <array>
+
+#include "modules/audio_processing/agc2/agc2_common.h"
+
+namespace webrtc {
+
+namespace test {
+
+// Parameters for interpolated gain curve using under-approximation to
+// avoid saturation.
+//
+// The saturation gain is defined in order to let hard-clipping occur for
+// those samples having a level that falls in the saturation region. It is an
+// upper bound of the actual gain to apply - i.e., that returned by the
+// limiter.
+
+// Knee and beyond-knee regions approximation parameters.
+// The gain curve is approximated as a piece-wise linear function.
+// |approx_params_x_| are the boundaries between adjacent linear pieces,
+// |approx_params_m_| and |approx_params_q_| are the slope and the y-intercept
+// values of each piece.
+struct InterpolatedParameters {
+  std::array<float, kInterpolatedGainCurveTotalPoints>
+      computed_approximation_params_x;
+  std::array<float, kInterpolatedGainCurveTotalPoints>
+      computed_approximation_params_m;
+  std::array<float, kInterpolatedGainCurveTotalPoints>
+      computed_approximation_params_q;
+};
+
+InterpolatedParameters ComputeInterpolatedGainCurveApproximationParams();
+}  // namespace test
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AGC2_COMPUTE_INTERPOLATED_GAIN_CURVE_H_