Log the freshness of the Variations seed in a histogram.

chrome/browser/metrics/variations/variations_service.cc

Index: chrome/browser/metrics/variations/variations_service.cc
diff --git a/chrome/browser/metrics/variations/variations_service.cc b/chrome/browser/metrics/variations/variations_service.cc
index 00c7816705d3638bc190824bbf3f7101bc93150f..4c95b077c35f676df2c10fc16e1c680acd707b52 100644
--- a/chrome/browser/metrics/variations/variations_service.cc
+++ b/chrome/browser/metrics/variations/variations_service.cc
@@ -177,6 +177,19 @@ bool VariationsService::CreateTrialsFromSeed() {
     }
   }
 
+  // Log the "freshness" of the seed that was just used. The freshness is the
+  // time between the last successful seed download and now.
+  const int64 last_fetch_time_internal =
+      local_state_->GetInt64(prefs::kVariationsLastFetchTime);
+  if (last_fetch_time_internal) {
+    const base::Time now = base::Time::Now();
+    const base::TimeDelta delta =
+        now - base::Time::FromInternalValue(last_fetch_time_internal);
+    // Log the value in number of minutes.
+    UMA_HISTOGRAM_CUSTOM_COUNTS("Variations.SeedFreshness", delta.InMinutes(),
+        1, base::TimeDelta::FromDays(30).InMinutes(), 50);
+  }
+
   return true;
 }
 
@@ -215,6 +228,7 @@ void VariationsService::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterStringPref(prefs::kVariationsSeed, std::string());
   registry->RegisterInt64Pref(prefs::kVariationsSeedDate,
                               base::Time().ToInternalValue());
+  registry->RegisterInt64Pref(prefs::kVariationsLastFetchTime, 0);
 }
 
 // static
@@ -290,6 +304,10 @@ void VariationsService::OnURLFetchComplete(const net::URLFetcher* source) {
     }
   }
 
+  if (response_code == net::HTTP_NOT_MODIFIED) {
+    RecordLastFetchTime();
+  }
+
   if (response_code != net::HTTP_OK) {
     DVLOG(1) << "Variations server request returned non-HTTP_OK response code: "
              << response_code;
@@ -348,6 +366,9 @@ bool VariationsService::StoreSeedData(const std::string& seed_data,
   local_prefs->SetInt64(prefs::kVariationsSeedDate,
                         seed_date.ToInternalValue());
   variations_serial_number_ = seed.serial_number();
+
+  RecordLastFetchTime();
+
   return true;
 }
 
@@ -601,4 +622,9 @@ void VariationsService::CreateTrialFromStudy(const Study& study,
     trial->Disable();
 }
 
+void VariationsService::RecordLastFetchTime() {
+  local_state_->SetInt64(prefs::kVariationsLastFetchTime,
+                         base::Time::Now().ToInternalValue());
+}
+
 }  // namespace chrome_variations