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.h

@@ -0,0 +1,45 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_VAD_GMM_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_VAD_GMM_H_
+
+namespace webrtc {
+
+// A structure that specifies a GMM.
+// A GMM is formulated as
+//  f(x) = w[0] * mixture[0] + w[1] * mixture[1] + ... +
+//         w[num_mixtures - 1] * mixture[num_mixtures - 1];
+// Where a 'mixture' is a Gaussian density.
+
+struct GmmParameters {
+  // weight[n] = log(w[n]) - |dimension|/2 * log(2*pi) - 1/2 * log(det(cov[n]));
+  // where cov[n] is the covariance matrix of mixture n;
+  const double* weight;
+  // pointer to the first element of a |num_mixtures|x|dimension| matrix
+  // where kth row is the mean of the kth mixture.
+  const double* mean;
+  // pointer to the first element of a |num_mixtures|x|dimension|x|dimension|
+  // 3D-matrix, where the kth 2D-matrix is the inverse of the covariance
+  // matrix of the kth mixture.
+  const double* covar_inverse;
+  // Dimensionality of the mixtures.
+  int dimension;
+  // number of the mixtures.
+  int num_mixtures;
+};
+
+// Evaluate the given GMM, according to |gmm_parameters|, at the given point
+// |x|. If the dimensionality of the given GMM is larger that the maximum
+// acceptable dimension by the following function -1 is returned.
+double EvaluateGmm(const double* x, const GmmParameters& gmm_parameters);
+
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_VAD_GMM_H_