Log the freshness of the Variations seed in a histogram.

chrome/browser/metrics/variations/variations_service.cc

 // 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.
 
 #include "chrome/browser/metrics/variations/variations_service.h"
 
 #include <set>
 
 #include "base/base64.h"
 #include "base/build_time.h"
@@ skipping 159 matching lines @@
     return false;
 
   chrome::VersionInfo::Channel channel = GetChannelForVariations();
   for (int i = 0; i < seed.study_size(); ++i) {
     if (ShouldAddStudy(seed.study(i), current_version_info, reference_date,
                        channel)) {
       CreateTrialFromStudy(seed.study(i), reference_date);
     }
   }
 
+  // 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;
 }
 
 void VariationsService::StartRepeatedVariationsSeedFetch() {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 
   // Check that |CreateTrialsFromSeed| was called, which is necessary to
   // retrieve the serial number that will be sent to the server.
   DCHECK(create_trials_from_seed_called_);
 
@@ skipping 18 matching lines @@
 
 void VariationsService::SetCreateTrialsFromSeedCalledForTesting(bool called) {
   create_trials_from_seed_called_ = called;
 }
 
 // static
 void VariationsService::RegisterPrefs(PrefRegistrySimple* registry) {
   registry->RegisterStringPref(prefs::kVariationsSeed, std::string());
   registry->RegisterInt64Pref(prefs::kVariationsSeedDate,
                               base::Time().ToInternalValue());
+  registry->RegisterInt64Pref(prefs::kVariationsLastFetchTime, 0);
 }
 
 // static
 VariationsService* VariationsService::Create(PrefService* local_state) {
 // This is temporarily disabled for Android. See http://crbug.com/168224
 #if !defined(GOOGLE_CHROME_BUILD) || defined(OS_ANDROID)
   // Unless the URL was provided, unsupported builds should return NULL to
   // indicate that the service should not be used.
   if (!CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kVariationsServerURL))
@@ skipping 53 matching lines @@
       response_code == net::HTTP_NOT_MODIFIED) {
     bool success = request->GetResponseHeaders()->GetDateValue(&response_date);
     DCHECK(success || response_date.is_null());
 
     if (!response_date.is_null()) {
       network_time_tracker_.UpdateNetworkTime(
           response_date,
           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) {
     DVLOG(1) << "Variations server request returned non-HTTP_OK response code: "
              << response_code;
     if (response_code == net::HTTP_NOT_MODIFIED)
       UMA_HISTOGRAM_MEDIUM_TIMES("Variations.FetchNotModifiedLatency", latency);
     else
       UMA_HISTOGRAM_MEDIUM_TIMES("Variations.FetchOtherLatency", latency);
     return;
@@ skipping 294 matching lines @@
                                       variation_id);
     }
   }
 
   trial->SetForced();
   if (IsStudyExpired(study, reference_date))
     trial->Disable();
 }
 
 }  // namespace chrome_variations