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/window_generator.h

@@ -0,0 +1,33 @@
+/*
+ *  Copyright (c) 2014 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_COMMON_AUDIO_WINDOW_GENERATOR_H_
+#define WEBRTC_COMMON_AUDIO_WINDOW_GENERATOR_H_
+
+#include <stddef.h>
+
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+// Helper class with generators for various signal transform windows.
+class WindowGenerator {
+ public:
+  static void Hanning(int length, float* window);
+  static void KaiserBesselDerived(float alpha, size_t length, float* window);
+
+ private:
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(WindowGenerator);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_COMMON_AUDIO_WINDOW_GENERATOR_H_
+