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/pitch_based_vad.h

@@ -0,0 +1,57 @@
+/*
+ *  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_PITCH_BASED_VAD_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_VAD_PITCH_BASED_VAD_H_
+
+#include "webrtc/base/scoped_ptr.h"
+#include "webrtc/modules/audio_processing/vad/common.h"
+#include "webrtc/modules/audio_processing/vad/gmm.h"
+#include "webrtc/typedefs.h"
+
+namespace webrtc {
+
+class AudioFrame;
+class VadCircularBuffer;
+
+// Computes the probability of the input audio frame to be active given
+// the corresponding pitch-gain and lag of the frame.
+class PitchBasedVad {
+ public:
+  PitchBasedVad();
+  ~PitchBasedVad();
+
+  // Compute pitch-based voicing probability, given the features.
+  //   features: a structure containing features required for computing voicing
+  //             probabilities.
+  //
+  //   p_combined: an array which contains the combined activity probabilities
+  //               computed prior to the call of this function. The method,
+  //               then, computes the voicing probabilities and combine them
+  //               with the given values. The result are returned in |p|.
+  int VoicingProbability(const AudioFeatures& features, double* p_combined);
+
+ private:
+  int UpdatePrior(double p);
+
+  // TODO(turajs): maybe defining this at a higher level (maybe enum) so that
+  // all the code recognize it as "no-error."
+  static const int kNoError = 0;
+
+  GmmParameters noise_gmm_;
+  GmmParameters voice_gmm_;
+
+  double p_prior_;
+
+  rtc::scoped_ptr<VadCircularBuffer> circular_buffer_;
+};
+
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_VAD_PITCH_BASED_VAD_H_