Fix dcheck in network_quality_estimator

Adding http_rtt_observation in ReadCachedNetworkQualityEstimate
causes notifying observers.
That can lead to calling ReadCachedNetworkQualityEstimate again.
So some observations can be added between adding
http_rtt_observation and adding transport_rtt_observation.
That ends up to breaking observations timestamp increasing.
To fix this we can use new timestamp each time when add
observation.
Same logic is used in AddDefaultEstimates for example.

R=ryansturm@chromium.org, tbansal@chromium.org

Bug: 841681
Change-Id: Ibed7d5e8e3efca82915d37b1de58df50ae43ff58
Reviewed-on: https://chromium-review.googlesource.com/1052690Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558609}

net/nqe/network_quality_estimator.cc

@@ -1357,8 +1357,6 @@ bool NetworkQualityEstimator::ReadCachedNetworkQualityEstimate() {
   nqe::internal::NetworkQuality network_quality =
       cached_network_quality.network_quality();
 
-  const base::TimeTicks now = tick_clock_->NowTicks();
-
   bool update_network_quality_store = false;
 
   // Populate |network_quality| with synthetic RTT and throughput observations
@@ -1387,25 +1385,25 @@ bool NetworkQualityEstimator::ReadCachedNetworkQualityEstimate() {
   }
 
   if (update_network_quality_store) {
-    network_quality_store_->Add(
-        current_network_id_,
-        nqe::internal::CachedNetworkQuality(now, network_quality,
-                                            effective_connection_type));
+    network_quality_store_->Add(current_network_id_,
+                                nqe::internal::CachedNetworkQuality(
+                                    tick_clock_->NowTicks(), network_quality,
+                                    effective_connection_type));
   }
 
   Observation http_rtt_observation(
-      network_quality.http_rtt().InMilliseconds(), now, INT32_MIN,
-      NETWORK_QUALITY_OBSERVATION_SOURCE_HTTP_CACHED_ESTIMATE);
+      network_quality.http_rtt().InMilliseconds(), tick_clock_->NowTicks(),
+      INT32_MIN, NETWORK_QUALITY_OBSERVATION_SOURCE_HTTP_CACHED_ESTIMATE);
   AddAndNotifyObserversOfRTT(http_rtt_observation);
 
   Observation transport_rtt_observation(
-      network_quality.transport_rtt().InMilliseconds(), now, INT32_MIN,
-      NETWORK_QUALITY_OBSERVATION_SOURCE_TRANSPORT_CACHED_ESTIMATE);
+      network_quality.transport_rtt().InMilliseconds(), tick_clock_->NowTicks(),
+      INT32_MIN, NETWORK_QUALITY_OBSERVATION_SOURCE_TRANSPORT_CACHED_ESTIMATE);
   AddAndNotifyObserversOfRTT(transport_rtt_observation);
 
   Observation througphput_observation(
-      network_quality.downstream_throughput_kbps(), now, INT32_MIN,
-      NETWORK_QUALITY_OBSERVATION_SOURCE_HTTP_CACHED_ESTIMATE);
+      network_quality.downstream_throughput_kbps(), tick_clock_->NowTicks(),
+      INT32_MIN, NETWORK_QUALITY_OBSERVATION_SOURCE_HTTP_CACHED_ESTIMATE);
   AddAndNotifyObserversOfThroughput(througphput_observation);
 
   ComputeEffectiveConnectionType();