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

webrtc/modules/audio_processing/agc2/gain_control2_unittest.cc

+/*
+ *  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.
+ */
+
+#include <memory>
+
+#include "webrtc/modules/audio_processing/agc2/gain_controller2.h"
+#include "webrtc/test/gtest.h"
+
+namespace webrtc {
+namespace test {
+
+TEST(GainController2, Instance) {
+  std::unique_ptr<GainController2> gain_controller2;
+  gain_controller2.reset(new GainController2());
+}
+
+}  // namespace test
+}  // namespace webrtc