Use request start time for estimating network quality.

net/base/network_quality_estimator.cc

 // Copyright 2015 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.
 
 #include "net/base/network_quality_estimator.h"
 
 #include <string>
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
@@ skipping 33 matching lines @@
   if (!request.url().is_valid() ||
       (!allow_localhost_requests_ && IsLocalhost(request.url().host())) ||
       !request.url().SchemeIsHTTPOrHTTPS() ||
       // Verify that response headers are received, so it can be ensured that
       // response is not cached.
       request.response_info().response_time.is_null() || request.was_cached() ||
       request.creation_time() < last_connection_change_) {
     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;
   }
 }
 
 void NetworkQualityEstimator::OnConnectionTypeChanged(
     NetworkChangeNotifier::ConnectionType type) {
   DCHECK(thread_checker_.CalledOnValidThread());
   if (bytes_read_since_last_connection_change_) {
     switch (current_connection_type_) {
@@ skipping 90 matching lines @@
   }
   if (!peak_kbps_since_last_connection_change_) {
     return NetworkQuality(fastest_RTT_since_last_connection_change_, 0.1,
                           peak_kbps_since_last_connection_change_, 0);
   }
   return NetworkQuality(fastest_RTT_since_last_connection_change_, 0.1,
                         peak_kbps_since_last_connection_change_, 0.1);
 }
 
 }  // namespace net