Measure time between secure time queries

components/network_time/network_time_tracker.cc

 // Copyright 2014 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 "components/network_time/network_time_tracker.h"
 
 #include <stdint.h>
 #include <string>
 #include <utility>
 
@@ skipping 516 matching lines @@
   }
 
   RecordFetchValidHistogram(true);
 
   // There is a "server_nonce" key here too, but it serves no purpose other than
   // to make the server's response unpredictable.
   base::Time current_time = base::Time::FromJsTime(current_time_millis);
   base::TimeDelta resolution =
       base::TimeDelta::FromMilliseconds(1) +
       base::TimeDelta::FromSeconds(kTimeServerMaxSkewSeconds);
+
+  // Record histograms for the latency of the time query and the time delta
+  // between time fetches.
   base::TimeDelta latency = tick_clock_->NowTicks() - fetch_started_;
   UMA_HISTOGRAM_TIMES("NetworkTimeTracker.TimeQueryLatency", latency);
+  if (!last_fetched_time_.is_null()) {
+    UMA_HISTOGRAM_CUSTOM_TIMES("NetworkTimeTracker.TimeBetweenFetches",
+                               current_time - last_fetched_time_,
+                               base::TimeDelta::FromHours(1),
+                               base::TimeDelta::FromDays(7), 50);
+  }
+  last_fetched_time_ = current_time;
+
   UpdateNetworkTime(current_time, resolution, latency, tick_clock_->NowTicks());
   return true;
 }
 
 void NetworkTimeTracker::OnURLFetchComplete(const net::URLFetcher* source) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(time_fetcher_);
   DCHECK_EQ(source, time_fetcher_.get());
 
   time_query_completed_ = true;
@@ skipping 40 matching lines @@
   base::Time network_time;
   if (GetNetworkTime(&network_time, nullptr) != NETWORK_TIME_AVAILABLE) {
     return true;
   }
 
   // Otherwise, make the decision at random.
   return base::RandDouble() < RandomQueryProbability();
 }
 
 }  // namespace network_time