NQE: Add Transport RTT based GetECT algorithm

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 102dfa766f16f43cde4fa5b2da8de03932c65708..afeca4eb01e1220879cb01bf87a644ebe06a9775 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -292,17 +292,20 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // at the HTTP layer measures the time from when the request was sent (this
   // happens after the connection is established) to the time when the response
   // headers were received.
+  // TODO(tbansal): Change it to return HTTP RTT as base::TimeDelta.
   virtual bool GetHttpRTTEstimate(base::TimeDelta* rtt) const
       WARN_UNUSED_RESULT;
 
   // Returns true if the RTT is available and sets |rtt| to the RTT estimated at
   // the transport layer. |rtt| should not be null. Virtualized for testing.
+  // TODO(tbansal): Change it to return transport RTT as base::TimeDelta.
   virtual bool GetTransportRTTEstimate(base::TimeDelta* rtt) const
       WARN_UNUSED_RESULT;
 
   // Returns true if downlink throughput is available and sets |kbps| to
   // estimated downlink throughput (in kilobits per second).
   // Virtualized for testing. |kbps| should not be null.
+  // TODO(tbansal): Change it to return throughput as int32.
   virtual bool GetDownlinkThroughputKbpsEstimate(int32_t* kbps) const;
 
   // Returns true if median RTT at the HTTP layer is available and sets |rtt|
@@ -311,6 +314,7 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // layer measures the time from when the request was sent (this happens after
   // the connection is established) to the time when the response headers were
   // received.
+  // TODO(tbansal): Change it to return HTTP RTT as base::TimeDelta.
   virtual bool GetRecentHttpRTTMedian(const base::TimeTicks& start_time,
                                       base::TimeDelta* rtt) const
       WARN_UNUSED_RESULT;
@@ -318,6 +322,7 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // Returns true if the median RTT at the transport layer is available and sets
   // |rtt| to the median of transport layer RTT observations since
   // |start_time|. |rtt| should not be null. Virtualized for testing.
+  // TODO(tbansal): Change it to return transport RTT as base::TimeDelta.
   virtual bool GetRecentTransportRTTMedian(const base::TimeTicks& start_time,
                                            base::TimeDelta* rtt) const
       WARN_UNUSED_RESULT;
@@ -326,6 +331,7 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // to the median of downstream throughput (in kilobits per second)
   // observations since |start_time|. Virtualized for testing. |kbps|
   // should not be null. Virtualized for testing.
+  // TODO(tbansal): Change it to return throughput as int32.
   virtual bool GetRecentMedianDownlinkThroughputKbps(
       const base::TimeTicks& start_time,
       int32_t* kbps) const WARN_UNUSED_RESULT;
@@ -372,10 +378,27 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // connection type.
   enum class EffectiveConnectionTypeAlgorithm {
     HTTP_RTT_AND_DOWNSTREAM_THROUGHOUT = 0,
+    TRANSPORT_RTT_OR_DOWNSTREAM_THROUGHOUT,
     EFFECTIVE_CONNECTION_TYPE_ALGORITHM_LAST
   };
 
+  // Defines how a metric (e.g, transport RTT) should be used when computing
+  // the effective connection type.
+  enum class MetricUsage {
+    // The metric should not be used when computing the effective connection
+    // type.
+    DO_NOT_USE = 0,
+    // If the metric is available, then it should be used when computing the
+    // effective connection type.
+    USE_IF_AVAILABLE,
+    // The metric is required when computing the effective connection type.
+    // If the value of the metric is unavailable, effective connection type
+    // should be set to |EFFECTIVE_CONNECTION_TYPE_UNKNOWN|.
+    MUST_BE_USED,
+  };
+
   // Map from algorithm names to EffectiveConnectionTypeAlgorithm.
+  // TODO(tbansal): Consider using an autogenerated enum using macros.
   const std::map<std::string, EffectiveConnectionTypeAlgorithm>
       algorithm_name_to_enum_;
 
@@ -483,12 +506,15 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   void UpdateSignalStrength();
 
   // Returns the effective type of the current connection based on only the
-  // samples observed after |start_time|. Uses HTTP RTT and downstream
-  // throughput to compute the effective connection type, and requires both of
-  // them to have a valid value.
-  EffectiveConnectionType
-  GetRecentEffectiveConnectionTypeHttpRTTAndDownstreamThroughput(
-      const base::TimeTicks& start_time) const;
+  // samples observed after |start_time|. May use HTTP RTT, transport RTT and
+  // downstream throughput to compute the effective connection type based on
+  // |http_rtt_metric|, |transport_rtt_metric| and
+  // |downstream_throughput_kbps_metric|, respectively.
+  EffectiveConnectionType GetRecentEffectiveConnectionTypeUsingMetrics(
+      const base::TimeTicks& start_time,
+      MetricUsage http_rtt_metric,
+      MetricUsage transport_rtt_metric,
+      MetricUsage downstream_throughput_kbps_metric) const;
 
   // Values of external estimate provider status. This enum must remain
   // synchronized with the enum of the same name in