Measure and log the latency of VariationsService requests.

chrome/browser/metrics/variations/variations_service.h

Index: chrome/browser/metrics/variations/variations_service.h
diff --git a/chrome/browser/metrics/variations/variations_service.h b/chrome/browser/metrics/variations/variations_service.h
index 4f55d4a012574d7f517b4c09feb7882fc49d7722..da1f371666e708435618d14318bd1e8c3ed37cdd 100644
--- a/chrome/browser/metrics/variations/variations_service.h
+++ b/chrome/browser/metrics/variations/variations_service.h
@@ -161,6 +161,10 @@ class VariationsService
   // 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