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/rms_level.cc

@@ -0,0 +1,61 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/audio_processing/rms_level.h"
+
+#include <assert.h>
+#include <math.h>
+
+namespace webrtc {
+
+static const float kMaxSquaredLevel = 32768 * 32768;
+
+RMSLevel::RMSLevel()
+    : sum_square_(0),
+      sample_count_(0) {}
+
+RMSLevel::~RMSLevel() {}
+
+void RMSLevel::Reset() {
+  sum_square_ = 0;
+  sample_count_ = 0;
+}
+
+void RMSLevel::Process(const int16_t* data, size_t length) {
+  for (size_t i = 0; i < length; ++i) {
+    sum_square_ += data[i] * data[i];
+  }
+  sample_count_ += length;
+}
+
+void RMSLevel::ProcessMuted(size_t length) {
+  sample_count_ += length;
+}
+
+int RMSLevel::RMS() {
+  if (sample_count_ == 0 || sum_square_ == 0) {
+    Reset();
+    return kMinLevel;
+  }
+
+  // Normalize by the max level.
+  float rms = sum_square_ / (sample_count_ * kMaxSquaredLevel);
+  // 20log_10(x^0.5) = 10log_10(x)
+  rms = 10 * log10(rms);
+  assert(rms <= 0);
+  if (rms < -kMinLevel)
+    rms = -kMinLevel;
+
+  rms = -rms;
+  Reset();
+  return static_cast<int>(rms + 0.5);
+}
+
+}  // namespace webrtc