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 e864c7e1f4619501fb8ce7073545f6f4c3ab7752..63b4afd86625d010ac5bea1c98522a5e24e19b3f 100644
--- a/net/base/network_quality_estimator.cc
+++ b/net/base/network_quality_estimator.cc
@@ -9,6 +9,7 @@
 
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
+#include "net/base/load_timing_info.h"
 #include "net/base/net_util.h"
 #include "net/base/network_quality.h"
 #include "net/url_request/url_request.h"
@@ -63,25 +64,50 @@ void NetworkQualityEstimator::NotifyDataReceived(
   }
 
   base::TimeTicks now = base::TimeTicks::Now();
-  base::TimeDelta request_duration = now - request.creation_time();
-  DCHECK_GE(request_duration, base::TimeDelta());
+  LoadTimingInfo load_timing_info;
+  request.GetLoadTimingInfo(&load_timing_info);
+
+  // Time when the resource was requested. Use the timings from LoadTimingInfo,
+  // if it is available since it is recorded after DNS is resolved and a secure
+  // connection is established.
+  base::TimeTicks request_start_time = !load_timing_info.send_start.is_null()

[mmenke, 2015/06/15 17:21:00]

Hrm...If load_timing_info.send_start or load_timing_info.receive_headers_end is
null, this request probably didn't go over the network (Or it was QUIC - not
sure if those are hooked up for QUIC yet).

May be better to just record nothing in those cases.

[tbansal1, 2015/06/15 18:57:11]

QUIC still has these 2 values populated. I checked by adding some
logging here:
https://code.google.com/p/chromium/codesearch#chromium/src/net/quic/quic_http...

+                                           ? load_timing_info.send_start
+                                           : request.creation_time();
+  DCHECK(!request_start_time.is_null());
+
+  // Time when the headers were received. Use timings from LoadTimingInfo, if
+  // available.
+  base::TimeTicks headers_received_time =
+      !load_timing_info.receive_headers_end.is_null()
+          ? load_timing_info.receive_headers_end
+          : now;
+  DCHECK(!headers_received_time.is_null());
+
+  // Duration between when the resource was requested and when response headers
+  // were received.
+  base::TimeDelta observed_rtt = headers_received_time - request_start_time;
+  DCHECK_GE(observed_rtt, base::TimeDelta());

[mmenke, 2015/06/15 17:21:00]

This is only used in the body of the next if statement, so should move it down
there.  (If you decide to subtract half of this from since_request_start for
better bandwidth measurement, of course, you'll need to move it back up here).

[tbansal1, 2015/06/15 18:57:11]

Done.

+
+  // Time since the resource was requested.
+  base::TimeDelta since_request_start = now - request_start_time;
+  DCHECK_GE(since_request_start, base::TimeDelta());
 
   // Only add RTT observation if this is the first read for this response.
   if (cumulative_prefilter_bytes_read == prefiltered_bytes_read) {
-    if (request_duration < fastest_rtt_since_last_connection_change_)
-      fastest_rtt_since_last_connection_change_ = request_duration;
+    if (observed_rtt < fastest_rtt_since_last_connection_change_)
+      fastest_rtt_since_last_connection_change_ = observed_rtt;
 
     rtt_msec_observations_.AddObservation(
-        Observation(request_duration.InMilliseconds(), now));
+        Observation(observed_rtt.InMilliseconds(), now));
   }
 
   // Ignore tiny transfers which will not produce accurate rates.
   // Ignore short duration transfers.
   if (cumulative_prefilter_bytes_read >= kMinTransferSizeInBytes &&
-      request_duration >=
+      since_request_start >=
           base::TimeDelta::FromMicroseconds(kMinRequestDurationMicroseconds)) {
     double kbps_f = cumulative_prefilter_bytes_read * 8.0 / 1000.0 /
-                    request_duration.InSecondsF();
+                    since_request_start.InSecondsF();
     DCHECK_GE(kbps_f, 0.0);
 
     // Check overflow errors. This may happen if the kbpsF is more than