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/vad/gmm.cc

@@ -0,0 +1,64 @@
+/*
+ *  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/vad/gmm.h"
+
+#include <math.h>
+#include <stdlib.h>
+
+#include "webrtc/typedefs.h"
+
+namespace webrtc {
+
+static const int kMaxDimension = 10;
+
+static void RemoveMean(const double* in,
+                       const double* mean_vec,
+                       int dimension,
+                       double* out) {
+  for (int n = 0; n < dimension; ++n)
+    out[n] = in[n] - mean_vec[n];
+}
+
+static double ComputeExponent(const double* in,
+                              const double* covar_inv,
+                              int dimension) {
+  double q = 0;
+  for (int i = 0; i < dimension; ++i) {
+    double v = 0;
+    for (int j = 0; j < dimension; j++)
+      v += (*covar_inv++) * in[j];
+    q += v * in[i];
+  }
+  q *= -0.5;
+  return q;
+}
+
+double EvaluateGmm(const double* x, const GmmParameters& gmm_parameters) {
+  if (gmm_parameters.dimension > kMaxDimension) {
+    return -1;  // This is invalid pdf so the caller can check this.
+  }
+  double f = 0;
+  double v[kMaxDimension];
+  const double* mean_vec = gmm_parameters.mean;
+  const double* covar_inv = gmm_parameters.covar_inverse;
+
+  for (int n = 0; n < gmm_parameters.num_mixtures; n++) {
+    RemoveMean(x, mean_vec, gmm_parameters.dimension, v);
+    double q = ComputeExponent(v, covar_inv, gmm_parameters.dimension) +
+               gmm_parameters.weight[n];
+    f += exp(q);
+    mean_vec += gmm_parameters.dimension;
+    covar_inv += gmm_parameters.dimension * gmm_parameters.dimension;
+  }
+  return f;
+}
+
+}  // namespace webrtc