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_internal.cc

@@ -0,0 +1,51 @@
+/*
+ *  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/pitch_internal.h"
+
+#include <cmath>
+
+// A 4-to-3 linear interpolation.
+// The interpolation constants are derived as following:
+// Input pitch parameters are updated every 7.5 ms. Within a 30-ms interval
+// we are interested in pitch parameters of 0-5 ms, 10-15ms and 20-25ms. This is
+// like interpolating 4-to-6 and keep the odd samples.
+// The reason behind this is that LPC coefficients are computed for the first
+// half of each 10ms interval.
+static void PitchInterpolation(double old_val, const double* in, double* out) {
+  out[0] = 1. / 6. * old_val + 5. / 6. * in[0];
+  out[1] = 5. / 6. * in[1] + 1. / 6. * in[2];
+  out[2] = 0.5 * in[2] + 0.5 * in[3];
+}
+
+void GetSubframesPitchParameters(int sampling_rate_hz,
+                                 double* gains,
+                                 double* lags,
+                                 int num_in_frames,
+                                 int num_out_frames,
+                                 double* log_old_gain,
+                                 double* old_lag,
+                                 double* log_pitch_gain,
+                                 double* pitch_lag_hz) {
+  // Gain interpolation is in log-domain, also returned in log-domain.
+  for (int n = 0; n < num_in_frames; n++)
+    gains[n] = log(gains[n] + 1e-12);
+
+  // Interpolate lags and gains.
+  PitchInterpolation(*log_old_gain, gains, log_pitch_gain);
+  *log_old_gain = gains[num_in_frames - 1];
+  PitchInterpolation(*old_lag, lags, pitch_lag_hz);
+  *old_lag = lags[num_in_frames - 1];
+
+  // Convert pitch-lags to Hertz.
+  for (int n = 0; n < num_out_frames; n++) {
+    pitch_lag_hz[n] = (sampling_rate_hz) / (pitch_lag_hz[n]);
+  }
+}