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/agc/gain_control.h

@@ -0,0 +1,105 @@
+/*
+ *  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_AGC_GAIN_CONTROL_H_
+#define MODULES_AUDIO_PROCESSING_AGC_GAIN_CONTROL_H_
+
+namespace webrtc {
+
+// The automatic gain control (AGC) component brings the signal to an
+// appropriate range. This is done by applying a digital gain directly and, in
+// the analog mode, prescribing an analog gain to be applied at the audio HAL.
+//
+// Recommended to be enabled on the client-side.
+class GainControl {
+ public:
+  // When an analog mode is set, this must be called prior to |ProcessStream()|
+  // to pass the current analog level from the audio HAL. Must be within the
+  // range provided to |set_analog_level_limits()|.
+  virtual int set_stream_analog_level(int level) = 0;
+
+  // When an analog mode is set, this should be called after |ProcessStream()|
+  // to obtain the recommended new analog level for the audio HAL. It is the
+  // users responsibility to apply this level.
+  virtual int stream_analog_level() const = 0;
+
+  enum Mode {
+    // Adaptive mode intended for use if an analog volume control is available
+    // on the capture device. It will require the user to provide coupling
+    // between the OS mixer controls and AGC through the |stream_analog_level()|
+    // functions.
+    //
+    // It consists of an analog gain prescription for the audio device and a
+    // digital compression stage.
+    kAdaptiveAnalog,
+
+    // Adaptive mode intended for situations in which an analog volume control
+    // is unavailable. It operates in a similar fashion to the adaptive analog
+    // mode, but with scaling instead applied in the digital domain. As with
+    // the analog mode, it additionally uses a digital compression stage.
+    kAdaptiveDigital,
+
+    // Fixed mode which enables only the digital compression stage also used by
+    // the two adaptive modes.
+    //
+    // It is distinguished from the adaptive modes by considering only a
+    // short time-window of the input signal. It applies a fixed gain through
+    // most of the input level range, and compresses (gradually reduces gain
+    // with increasing level) the input signal at higher levels. This mode is
+    // preferred on embedded devices where the capture signal level is
+    // predictable, so that a known gain can be applied.
+    kFixedDigital
+  };
+
+  virtual int set_mode(Mode mode) = 0;
+  virtual Mode mode() const = 0;
+
+  // Sets the target peak |level| (or envelope) of the AGC in dBFs (decibels
+  // from digital full-scale). The convention is to use positive values. For
+  // instance, passing in a value of 3 corresponds to -3 dBFs, or a target
+  // level 3 dB below full-scale. Limited to [0, 31].
+  //
+  // TODO(ajm): use a negative value here instead, if/when VoE will similarly
+  //            update its interface.
+  virtual int set_target_level_dbfs(int level) = 0;
+  virtual int target_level_dbfs() const = 0;
+
+  // Sets the maximum |gain| the digital compression stage may apply, in dB. A
+  // higher number corresponds to greater compression, while a value of 0 will
+  // leave the signal uncompressed. Limited to [0, 90].
+  virtual int set_compression_gain_db(int gain) = 0;
+  virtual int compression_gain_db() const = 0;
+
+  // When enabled, the compression stage will hard limit the signal to the
+  // target level. Otherwise, the signal will be compressed but not limited
+  // above the target level.
+  virtual int enable_limiter(bool enable) = 0;
+  virtual bool is_limiter_enabled() const = 0;
+
+  // Sets the |minimum| and |maximum| analog levels of the audio capture device.
+  // Must be set if and only if an analog mode is used. Limited to [0, 65535].
+  virtual int set_analog_level_limits(int minimum, int maximum) = 0;
+  virtual int analog_level_minimum() const = 0;
+  virtual int analog_level_maximum() const = 0;
+
+  // Returns true if the AGC has detected a saturation event (period where the
+  // signal reaches digital full-scale) in the current frame and the analog
+  // level cannot be reduced.
+  //
+  // This could be used as an indicator to reduce or disable analog mic gain at
+  // the audio HAL.
+  virtual bool stream_is_saturated() const = 0;
+
+ protected:
+  virtual ~GainControl() {}
+};
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AGC_GAIN_CONTROL_H_