Create a synthetic field trial for precache

components/precache/content/precache_manager.cc

 // Copyright 2013 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 "components/precache/content/precache_manager.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
@@ skipping 33 matching lines @@
 
 size_t NumTopHosts() {
   return kNumTopHosts;
 }
 
 PrecacheManager::PrecacheManager(
     content::BrowserContext* browser_context,
     const syncer::SyncService* const sync_service,
     const history::HistoryService* const history_service,
     const base::FilePath& db_path,
-    std::unique_ptr<PrecacheDatabase> precache_database)
+    std::unique_ptr<PrecacheDatabase> precache_database,
+    const base::Callback<void(const base::Time&)>&
+        register_synthetic_field_trial_callback)
     : browser_context_(browser_context),
       sync_service_(sync_service),
       history_service_(history_service),
-      is_precaching_(false) {
+      is_precaching_(false),
+      register_synthetic_field_trial_callback_(
+          register_synthetic_field_trial_callback) {
   precache_database_ = std::move(precache_database);
   BrowserThread::PostTask(
       BrowserThread::DB, FROM_HERE,
       base::Bind(base::IgnoreResult(&PrecacheDatabase::Init),
                  base::Unretained(precache_database_.get()), db_path));
+  BrowserThread::PostTaskAndReplyWithResult(

[twifkak, 2016/12/08 21:49:22]

Good idea, sticking it in the PrecacheManager constructor.

+      BrowserThread::DB, FROM_HERE,
+      base::Bind(&PrecacheDatabase::GetLastPrecacheTimestamp,
+                 base::Unretained(precache_database_.get())),
+      base::Bind(&PrecacheManager::RegisterSyntheticFieldTrial, AsWeakPtr()));
 }
 
 PrecacheManager::~PrecacheManager() {
   // DeleteSoon posts a non-nestable task to the task runner, so any previously
   // posted tasks that rely on an Unretained precache_database_ will finish
   // before it is deleted.
   BrowserThread::DeleteSoon(BrowserThread::DB, FROM_HERE,
                             precache_database_.release());
 }
 
+void PrecacheManager::RegisterSyntheticFieldTrial(
+    const base::Time& last_precache_time) {
+  register_synthetic_field_trial_callback_.Run(last_precache_time);
+}
+
 bool PrecacheManager::IsInExperimentGroup() const {
   // Verify IsPrecachingAllowed() before calling FieldTrialList::FindFullName().
   // This is because field trials are only assigned when requested. This allows
   // us to create Control and Experiment groups that are limited to users for
   // whom PrecachingAllowed() is true, thus accentuating the impact of
   // precaching.
   return IsPrecachingAllowed() &&
          (base::StartsWith(
               base::FieldTrialList::FindFullName(kPrecacheFieldTrialName),
               kPrecacheFieldTrialEnabledGroup, base::CompareCase::SENSITIVE) ||
@@ skipping 271 matching lines @@
       this));
   precache_fetcher_->Start();
 }
 
 void PrecacheManager::OnHostsReceivedThenDone(
     const history::TopHostsList& host_counts) {
   OnDone();
 }
 
 }  // namespace precache