Measure and log the latency of VariationsService requests.

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 165 matching lines @@
   pending_seed_request_->SetLoadFlags(net::LOAD_DO_NOT_SEND_COOKIES |
                                       net::LOAD_DO_NOT_SAVE_COOKIES);
   pending_seed_request_->SetRequestContext(
       g_browser_process->system_request_context());
   pending_seed_request_->SetMaxRetries(kMaxRetrySeedFetch);
   if (!variations_serial_number_.empty()) {
     pending_seed_request_->AddExtraRequestHeader("If-Match:" +
                                                  variations_serial_number_);
   }
   pending_seed_request_->Start();
+
+  last_request_started_time_ = base::TimeTicks::Now();
 }
 
 void VariationsService::FetchVariationsSeed() {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 
   if (!resource_request_allowed_notifier_->ResourceRequestsAllowed()) {
     DVLOG(1) << "Resource requests were not allowed. Waiting for notification.";
     return;
   }
 
   DoActualFetch();
 }
 
 void VariationsService::OnURLFetchComplete(const net::URLFetcher* source) {
   DCHECK_EQ(pending_seed_request_.get(), source);
   // The fetcher will be deleted when the request is handled.
   scoped_ptr<const net::URLFetcher> request(
       pending_seed_request_.release());
   if (request->GetStatus().status() != net::URLRequestStatus::SUCCESS) {
     DVLOG(1) << "Variations server request failed.";
     return;
   }
 
   // Log the response code.
   UMA_HISTOGRAM_CUSTOM_ENUMERATION("Variations.SeedFetchResponseCode",
       net::HttpUtil::MapStatusCodeForHistogram(request->GetResponseCode()),
       net::HttpUtil::GetStatusCodesForHistogram());
 
+  const base::TimeDelta latency =
+      base::TimeTicks::Now() - last_request_started_time_;
+
   if (request->GetResponseCode() != 200) {
     DVLOG(1) << "Variations server request returned non-200 response code: "
              << request->GetResponseCode();
+    if (request->GetResponseCode() == 304)
+      UMA_HISTOGRAM_MEDIUM_TIMES("Variations.FetchNotModifiedLatency", latency);
+    else
+      UMA_HISTOGRAM_MEDIUM_TIMES("Variations.FetchOtherLatency", latency);
     return;
   }
+  UMA_HISTOGRAM_MEDIUM_TIMES("Variations.FetchSuccessLatency", latency);
 
   std::string seed_data;
   bool success = request->GetResponseAsString(&seed_data);
   DCHECK(success);
 
   base::Time response_date;
   success = request->GetResponseHeaders()->GetDateValue(&response_date);
   DCHECK(success || response_date.is_null());
 
   StoreSeedData(seed_data, response_date, g_browser_process->local_state());
@@ skipping 271 matching lines @@
                                       variation_id);
     }
   }
 
   trial->SetForced();
   if (IsStudyExpired(study, reference_date))
     trial->Disable();
 }
 
 }  // namespace chrome_variations