Measure and log the latency of VariationsService requests.

chrome/browser/metrics/variations/variations_service.h

 // Copyright (c) 2012 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.
 
 #ifndef CHROME_BROWSER_METRICS_VARIATIONS_VARIATIONS_SERVICE_H_
 #define CHROME_BROWSER_METRICS_VARIATIONS_VARIATIONS_SERVICE_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
@@ skipping 143 matching lines @@
   bool create_trials_from_seed_called_;
 
   // The timer used to repeatedly ping the server. Keep this as an instance
   // member so if VariationsService goes out of scope, the timer is
   // automatically canceled.
   base::RepeatingTimer<VariationsService> timer_;
 
   // Helper class used to tell this service if it's allowed to make network
   // resource requests.
   scoped_ptr<ResourceRequestAllowedNotifier> resource_request_allowed_notifier_;
+
+  // The start time of the last seed request. This is used to measure the
+  // latency of seed requests. Initially zero.
+  base::TimeTicks last_request_started_time_;
 };
 
 }  // namespace chrome_variations
 
 #endif  // CHROME_BROWSER_METRICS_VARIATIONS_VARIATIONS_SERVICE_H_