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..54165c907d2565e214777bfeac826651388f2f55 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
@@ -288,6 +302,10 @@ void VariationsService::OnURLFetchComplete(const net::URLFetcher* source) {
           base::TimeDelta::FromMilliseconds(kServerTimeResolutionMs),
           latency);
     }
+
+    // Record the time of the most recent successful fetch.
+    local_state_->SetInt64(prefs::kVariationsLastFetchTime,

[Alexei Svitkine (slow), 2013/02/22 18:46:51]

Hmm, one little issue with doing this here is that it won't catch the case where
there's an early return in StoreSeedData() - e.g. if the server replied with 200
but the payload was bad.

But we can't just move this snippet there because it won't catch the 304 case.

How about making this a separate function and calling from this function for the
304 case and from the end of StoreSeedData in the 200 other case?

[SteveT, 2013/02/22 20:15:36]

What do you think of this latest change? Another option is to make it a
anonymous namespace function that takes Local State as a param. Not sure which
you may prefer (I don't think this is prohibited)

+                           base::Time::Now().ToInternalValue());
   }
 
   if (response_code != net::HTTP_OK) {