AGC2 as a new APM sub-module operating with hard-coded gain.

webrtc/modules/audio_processing/agc2/gain_controller2.h

+/*
+ *  Copyright (c) 2017 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 WEBRTC_MODULES_AUDIO_PROCESSING_AGC2_GAIN_CONTROLLER2_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_AGC2_GAIN_CONTROLLER2_H_
+
+#include <string>
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/modules/audio_processing/include/audio_processing.h"
+
+namespace webrtc {
+
+// Gain Controller 2 is an alternative gain control module that will entirely

[peah-webrtc, 2017/05/05 20:44:10]

I'd prefer a comment which describes what the class is/does and does not refer
to the current AGC. 

[AleBzk, 2017/05/16 12:38:43]

Done.

+// replace the existing AGC, the implementation of which is distributed across
+// several classes (namely, GainControlImpl, GainControlForExperimentalAgc,
+// AgcManagerDirect and Agc).
+// Gain Control 2 temporarily implements the fixed gain mode only, and it has
+// the following features:
+// - not operating in the band split domain;
+// - implemented with floating point.
+class GainController2 {
+ public:
+  GainController2();
+  ~GainController2();
+
+  static bool Validate(const AudioProcessing::Config::GainController2& config);
+  static std::string ToString(
+      const AudioProcessing::Config::GainController2& config);
+
+ private:
+  RTC_DISALLOW_COPY_AND_ASSIGN(GainController2);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_AGC2_GAIN_CONTROLLER2_H_