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/system_wrappers/source/thread_posix.h

@@ -0,0 +1,53 @@
+/*
+ *  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_SYSTEM_WRAPPERS_SOURCE_THREAD_POSIX_H_
+#define WEBRTC_SYSTEM_WRAPPERS_SOURCE_THREAD_POSIX_H_
+
+#include "webrtc/base/event.h"
+#include "webrtc/base/scoped_ptr.h"
+#include "webrtc/base/thread_checker.h"
+#include "webrtc/system_wrappers/interface/thread_wrapper.h"
+
+#include <pthread.h>
+
+namespace webrtc {
+
+int ConvertToSystemPriority(ThreadPriority priority, int min_prio,
+                            int max_prio);
+
+class ThreadPosix : public ThreadWrapper {
+ public:
+  ThreadPosix(ThreadRunFunction func, void* obj, const char* thread_name);
+  ~ThreadPosix() override;
+
+  // From ThreadWrapper.
+  bool Start() override;
+  bool Stop() override;
+
+  bool SetPriority(ThreadPriority priority) override;
+
+ private:
+  static void* StartThread(void* param);
+
+  void Run();
+
+  rtc::ThreadChecker thread_checker_;
+  ThreadRunFunction const run_function_;
+  void* const obj_;
+  rtc::Event stop_event_;
+  const std::string name_;
+
+  pthread_t thread_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_SYSTEM_WRAPPERS_SOURCE_THREAD_POSIX_H_