Implement THROTTLED priority semantics.

net/base/quantile_estimator.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_QUANTILE_ESTIMATOR_

[Charlie Harrison, 2016/09/01 18:17:53]

ESTIMATOR_H_

[Randy Smith (Not in Mondays), 2016/09/18 19:12:35]

Ooops; thank you.  Done.

+#define NET_BASE_QUANTILE_ESTIMATOR_
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+// This class estimates statistical quantiles (e.g. 10%l, 50%l) for
+// distributions presented in stream form.  These estimates adjust
+// automatically when the stream distribution changes.
+class NET_EXPORT QuantileEstimator {
+ public:
+  using RandomNumberCallback = base::Callback<int(void)>;
+
+  // |quantile| is a number between 0 and 100 indicating what quantile
+  // should be estimated (e.g. 50 would be a median estimate).
+  // |initial_estimate| is the value the class is seeded with; in other
+  // words, if AddSample() is never called,
+  // |CurrentEstimate() == initial_estimate|.
+  QuantileEstimator(int quantile, int initial_estimate);

[Charlie Harrison, 2016/09/01 18:17:53]

I wonder if there should be justification for this class operating on integers
only?

[Randy Smith (Not in Mondays), 2016/09/18 19:12:35]

It was mostly because I didn't need it to operate on floating point for my
purposes, and I distrust floating point arithmetic.  If someone else wants to
extend it to floating point they can.  

But I'm not sure how to write that in a comment.  I've put in a TODO that tries
to encapsulate the issues; let me know what you think.

+
+  ~QuantileEstimator();
+
+  int current_estimate() const { return current_estimate_; }
+  void AddSample(int sample);
+
+  // Specify a callback that will generator a "random" number

[Charlie Harrison, 2016/09/01 18:17:53]

s/generator/generate

[Randy Smith (Not in Mondays), 2016/09/18 19:12:35]

Done.

+  // in the range [0,99] on each call.  Used so that tests can
+  // rely on reproducible behavior.
+  void SetRandomNumberGeneratorForTesting(
+      RandomNumberCallback generator_callback);
+
+ private:
+  const int quantile_;
+
+  bool sign_positive_;
+  int current_estimate_;
+  int current_step_;
+
+  RandomNumberCallback generator_callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(QuantileEstimator);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_QUANTILE_ESTIMATOR_