Make the BWE threshold adaptive.

webrtc/modules/remote_bitrate_estimator/test/random.cc

+/*
+ *  Copyright (c) 2015 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/remote_bitrate_estimator/test/random.h"
+
+#include <math.h>
+
+Random::Random(uint32_t seed) : a_(0x531FDB97 ^ seed), b_(0x6420ECA8 + seed) {
+}
+
+float Random::Rand() {
+  const float kScale = 1.0f / 0xffffffff;
+  float result = kScale * b_;
+  a_ ^= b_;
+  b_ += a_;
+  return result;
+}
+
+int Random::Gaussian(int mean, int standard_deviation) {
+  // Creating a Normal distribution variable from two independent uniform
+  // variables based on the Box-Muller transform, which is defined on the
+  // interval (0, 1], hence the mask+add below.
+  const double kPi = 3.14159265358979323846;
+  const double kScale = 1.0 / 0x80000000ul;
+  double u1 = kScale * ((a_ & 0x7ffffffful) + 1);
+  double u2 = kScale * ((b_ & 0x7ffffffful) + 1);
+  a_ ^= b_;
+  b_ += a_;
+  return static_cast<int>(
+      mean + standard_deviation * sqrt(-2 * log(u1)) * cos(2 * kPi * u2));
+}