Create a synthetic field trial for precache.

chrome/browser/precache/precache_util.cc

 // Copyright 2016 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/precache/precache_util.h"
 
+#include <string>
+#include <vector>
+
+#include "base/metrics/field_trial.h"
 #include "base/time/time.h"
 #include "chrome/browser/browser_process.h"
+#include "chrome/browser/metrics/chrome_metrics_service_accessor.h"
 #include "chrome/browser/precache/precache_manager_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "components/data_use_measurement/content/content_url_request_classifier.h"
 #include "components/precache/content/precache_manager.h"
 #include "content/public/browser/browser_thread.h"
 #include "net/url_request/url_request.h"
 #include "url/gurl.h"
 
 namespace net {
 class HttpResponseInfo;
 }
 
 namespace {
 
+const char kPrecacheSynthetic15D[] = "PrecacheSynthetic15D";
+const char kPrecacheSynthetic1D[] = "PrecacheSynthetic1D";
+
 void UpdatePrecacheMetricsAndStateOnUIThread(const GURL& url,
                                              const GURL& referrer,
                                              base::TimeDelta latency,
                                              const base::Time& fetch_time,
                                              const net::HttpResponseInfo& info,
                                              int64_t size,
                                              bool is_user_traffic,
                                              void* profile_id) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 
   if (!g_browser_process->profile_manager()->IsValidProfile(profile_id))
     return;
   Profile* profile = reinterpret_cast<Profile*>(profile_id);
 
   precache::PrecacheManager* precache_manager =
       precache::PrecacheManagerFactory::GetForBrowserContext(profile);
   // |precache_manager| could be NULL if the profile is off the record.
   if (!precache_manager || !precache_manager->IsPrecachingAllowed())
     return;
 
   precache_manager->UpdatePrecacheMetricsAndState(
-      url, referrer, latency, fetch_time, info, size, is_user_traffic);
+      url, referrer, latency, fetch_time, info, size, is_user_traffic,
+      base::Bind(&precache::RegisterPrecacheSyntheticFieldTrial));
 }
 
 }  // namespace
 
 namespace precache {
 
 // TODO(rajendrant): Add unittests for this function.
 void UpdatePrecacheMetricsAndState(const net::URLRequest* request,
                                    void* profile_id) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
 
   // For better accuracy, we use the actual bytes read instead of the length
   // specified with the Content-Length header, which may be inaccurate,
   // or missing, as is the case with chunked encoding.
   int64_t received_content_length = request->received_response_content_length();
   base::TimeDelta latency = base::TimeTicks::Now() - request->creation_time();
 
   // Record precache metrics when a fetch is completed successfully, if
   // precaching is allowed.
   content::BrowserThread::PostTask(
       content::BrowserThread::UI, FROM_HERE,
       base::Bind(&UpdatePrecacheMetricsAndStateOnUIThread, request->url(),
                  GURL(request->referrer()), latency, base::Time::Now(),
                  request->response_info(), received_content_length,
                  data_use_measurement::IsUserRequest(*request), profile_id));
 }
 
+// |last_precache_time| is the last time precache task was run.
+void RegisterPrecacheSyntheticFieldTrial(base::Time last_precache_time) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+
+  std::vector<uint32_t> groups;
+  base::TimeDelta time_ago = base::Time::Now() - last_precache_time;
+  // Look up the current group name (e.g. Control or Enabled).
+  std::string group_name =
+      base::FieldTrialList::FindFullName(kPrecacheFieldTrialName);
+  // group_name should only be empty if the Precache trial does not exist.
+  if (!group_name.empty()) {
+    // Register matching synthetic trials for 15-day and 1-day candidates.
+    if (time_ago <= base::TimeDelta::FromDays(15))
+      ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+          kPrecacheSynthetic15D, group_name);
+    if (time_ago <= base::TimeDelta::FromDays(1))
+      ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+          kPrecacheSynthetic1D, group_name);
+  }
+}
+
 }  // namespace precache