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/common_audio/resampler/sinusoidal_linear_chirp_source.cc

@@ -0,0 +1,58 @@
+/*
+ *  Copyright (c) 2013 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.
+ */
+
+// MSVC++ requires this to be set before any other includes to get M_PI.
+#define _USE_MATH_DEFINES
+
+#include "webrtc/common_audio/resampler/sinusoidal_linear_chirp_source.h"
+
+#include <math.h>
+
+namespace webrtc {
+
+SinusoidalLinearChirpSource::SinusoidalLinearChirpSource(int sample_rate,
+                                                         size_t samples,
+                                                         double max_frequency,
+                                                         double delay_samples)
+    : sample_rate_(sample_rate),
+      total_samples_(samples),
+      max_frequency_(max_frequency),
+      current_index_(0),
+      delay_samples_(delay_samples) {
+  // Chirp rate.
+  double duration = static_cast<double>(total_samples_) / sample_rate_;
+  k_ = (max_frequency_ - kMinFrequency) / duration;
+}
+
+void SinusoidalLinearChirpSource::Run(size_t frames, float* destination) {
+  for (size_t i = 0; i < frames; ++i, ++current_index_) {
+    // Filter out frequencies higher than Nyquist.
+    if (Frequency(current_index_) > 0.5 * sample_rate_) {
+      destination[i] = 0;
+    } else {
+      // Calculate time in seconds.
+      if (current_index_ < delay_samples_) {
+        destination[i] = 0;
+      } else {
+        // Sinusoidal linear chirp.
+        double t = (current_index_ - delay_samples_) / sample_rate_;
+        destination[i] =
+            sin(2 * M_PI * (kMinFrequency * t + (k_ / 2) * t * t));
+      }
+    }
+  }
+}
+
+double SinusoidalLinearChirpSource::Frequency(size_t position) {
+  return kMinFrequency + (position - delay_samples_) *
+      (max_frequency_ - kMinFrequency) / total_samples_;
+}
+
+}  // namespace webrtc