Use request start time for estimating network quality.

net/base/network_quality_estimator.cc

Index: net/base/network_quality_estimator.cc
diff --git a/net/base/network_quality_estimator.cc b/net/base/network_quality_estimator.cc
index 6415ee6e6d7eb36b47ab4fd568d3537283b27729..94119e611083829861c2d9d7d1e3435e1c6b1e3d 100644
--- a/net/base/network_quality_estimator.cc
+++ b/net/base/network_quality_estimator.cc
@@ -51,23 +51,37 @@ void NetworkQualityEstimator::NotifyDataReceived(const URLRequest& request,
     return;
   }
 
-  base::TimeTicks now = base::TimeTicks::Now();
-  base::TimeDelta request_duration = now - request.creation_time();
-  DCHECK_GE(request_duration, base::TimeDelta());
+  base::Time now = base::Time::Now();
+
+  // Time when the resource was requested.

[bengr, 2015/06/09 00:18:49]

Please add a comment to explain this logic.

[tbansal1, 2015/06/10 18:20:11]

Done.

+  base::Time request_start_time = !request.request_time().is_null()
+                                      ? request.request_time()
+                                      : request.creation_time();
+
+  // Difference of when the response headers were received and when the resource

[bengr, 2015/06/09 00:18:49]

// Duration between when the resource was requested and when response headers
were received.

[tbansal1, 2015/06/10 18:20:11]

Done.

+  // was requested.
+  base::TimeDelta estimated_rtt =

[bengr, 2015/06/09 00:18:49]

Maybe rename this as observed_rtt? It would be good if our samples were called
observations, and the estimates we report were called estimates.

[tbansal1, 2015/06/10 18:20:11]

Done.

+      request.response_info().response_time - request_start_time;

[bengr, 2015/06/09 00:18:49]

Can response_time be null?

[tbansal1, 2015/06/10 18:20:11]

No, there is a check above in the "if" condition:
request.response_info().response_time.is_null() 
then, return

+  DCHECK_GE(estimated_rtt, base::TimeDelta());
+
+  // Time since the resource was requested.
+  base::TimeDelta since_request_start = now - request_start_time;
+  DCHECK_GE(since_request_start, base::TimeDelta());
+
   if (!bytes_read_since_last_connection_change_)
-    fastest_RTT_since_last_connection_change_ = request_duration;
+    fastest_RTT_since_last_connection_change_ = estimated_rtt;
 
   bytes_read_since_last_connection_change_ = true;
-  if (request_duration < fastest_RTT_since_last_connection_change_)
-    fastest_RTT_since_last_connection_change_ = request_duration;
+  if (estimated_rtt < fastest_RTT_since_last_connection_change_)
+    fastest_RTT_since_last_connection_change_ = estimated_rtt;
 
   // Ignore tiny transfers which will not produce accurate rates.
   // Ignore short duration transfers.
   if (prefilter_bytes_read >= kMinTransferSizeInBytes &&
-      request_duration >=
+      since_request_start >=
           base::TimeDelta::FromMicroseconds(kMinRequestDurationMicroseconds)) {
     uint64_t kbps = static_cast<uint64_t>(prefilter_bytes_read * 8 * 1000 /
-                                          request_duration.InMicroseconds());
+                                          since_request_start.InMicroseconds());
     if (kbps > peak_kbps_since_last_connection_change_)
       peak_kbps_since_last_connection_change_ = kbps;
   }