Log the freshness of the Variations seed in a histogram.

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 5066ccbf56b20245610d464a850405784bd5f34a..ac5f08f4c79cac7712b7f1e4f619b414e5c3e74f 100644
--- a/chrome/browser/metrics/variations/variations_service.h
+++ b/chrome/browser/metrics/variations/variations_service.h
@@ -164,6 +164,9 @@ class VariationsService
   void CreateTrialFromStudy(const Study& study,
                             const base::Time& reference_date);
 
+  // Record the time of the most recent successful fetch.
+  void RecordLastFetchTime();
+
   // The pref service used to store persist the variations seed.
   PrefService* local_state_;