Update audio_processing module

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Pull in third party license file

 * Replace .gypi files with BUILD.gn to keep track of what changes
   upstream

 * Bunch of new filse pulled in as dependencies

 * Won't build yet due to changes needed on top of these

webrtc/modules/audio_processing/agc/utility.cc

@@ -0,0 +1,35 @@
+/*
+ *  Copyright (c) 2012 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 "webrtc/modules/audio_processing/agc/utility.h"
+
+#include <math.h>
+
+static const double kLog10 = 2.30258509299;
+static const double kLinear2DbScale = 20.0 / kLog10;
+static const double kLinear2LoudnessScale = 13.4 / kLog10;
+
+double Loudness2Db(double loudness) {
+  return loudness * kLinear2DbScale / kLinear2LoudnessScale;
+}
+
+double Linear2Loudness(double rms) {
+  if (rms == 0)
+    return -15;
+  return kLinear2LoudnessScale * log(rms);
+}
+
+double Db2Loudness(double db) {
+  return db * kLinear2LoudnessScale / kLinear2DbScale;
+}
+
+double Dbfs2Loudness(double dbfs) {
+  return Db2Loudness(90 + dbfs);
+}