NQE: Record correlation metric in UMA

net/nqe/network_quality_estimator.h

Index: net/nqe/network_quality_estimator.h
diff --git a/net/nqe/network_quality_estimator.h b/net/nqe/network_quality_estimator.h
index c13ae601061a48b6c536a81b12f53ba7cc71ba39..410119f0b20de15d264708944c31731caca4e308 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -502,6 +502,11 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   void RecordExternalEstimateProviderMetrics(
       NQEExternalEstimateProviderStatus status) const;
 
+  // Records correlation metric that can be used for computing the correlation

[bengr, 2016/07/08 16:49:52]

Records -> Records a
HTTP -> HTTP-layer
transport -> transport-layer

What does "time taken to fetch |request|" mean?

[tbansal1, 2016/07/08 17:45:51]

Done.
Re-worded. Not sure it is useful to explain more (code is pretty obvious).

+  // between HTTP RTT, transport RTT, throughput and the time taken to fetch
+  // |request|.
+  void RecordCorrelationMetric(const URLRequest& request) const;
+
   // Determines if the requests to local host can be used in estimating the
   // network quality. Set to true only for tests.
   bool use_localhost_requests_;
@@ -604,6 +609,12 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // |effective_connection_type_recomputation_interval_| ago).
   EffectiveConnectionType effective_connection_type_;
 
+  // Correlation UMA is recorded with |correlation_logging_probability_|
+  // probability. e.g., if it is 0.0, then the UMA will never be recorded. On
+  // the other hand, if it is 1.0, then it will be recorded for all valid HTTP
+  // requests.

[bengr, 2016/07/08 16:49:52]

Why is it not recorded for all requests? If this is a performance optimization,
say so, and also provide some intuitions as to why performance would suffer with
a 1.0 probability.

[tbansal1, 2016/07/08 17:45:51]

Added more comments.

+  const double correlation_logging_probability_;

[bengr, 2016/07/08 16:49:52]

rename: correlation_uma_reporting_probability_;

[tbansal1, 2016/07/08 17:45:51]

Done.

+
   base::ThreadChecker thread_checker_;
 
   base::WeakPtrFactory<NetworkQualityEstimator> weak_ptr_factory_;