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.h

@@ -0,0 +1,55 @@
+/*
+ *  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.
+ */
+
+// Modified from the Chromium original here:
+// src/media/base/sinc_resampler_unittest.cc
+
+#ifndef WEBRTC_COMMON_AUDIO_RESAMPLER_SINUSOIDAL_LINEAR_CHIRP_SOURCE_H_
+#define WEBRTC_COMMON_AUDIO_RESAMPLER_SINUSOIDAL_LINEAR_CHIRP_SOURCE_H_
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/common_audio/resampler/sinc_resampler.h"
+
+namespace webrtc {
+
+// Fake audio source for testing the resampler.  Generates a sinusoidal linear
+// chirp (http://en.wikipedia.org/wiki/Chirp) which can be tuned to stress the
+// resampler for the specific sample rate conversion being used.
+class SinusoidalLinearChirpSource : public SincResamplerCallback {
+ public:
+  // |delay_samples| can be used to insert a fractional sample delay into the
+  // source.  It will produce zeros until non-negative time is reached.
+  SinusoidalLinearChirpSource(int sample_rate, size_t samples,
+                              double max_frequency, double delay_samples);
+
+  virtual ~SinusoidalLinearChirpSource() {}
+
+  void Run(size_t frames, float* destination) override;
+
+  double Frequency(size_t position);
+
+ private:
+  enum {
+    kMinFrequency = 5
+  };
+
+  int sample_rate_;
+  size_t total_samples_;
+  double max_frequency_;
+  double k_;
+  size_t current_index_;
+  double delay_samples_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(SinusoidalLinearChirpSource);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_COMMON_AUDIO_RESAMPLER_SINUSOIDAL_LINEAR_CHIRP_SOURCE_H_