Create a synthetic field trial for precache

components/precache/content/precache_manager.h

 // 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.
 
 #ifndef COMPONENTS_PRECACHE_CONTENT_PRECACHE_MANAGER_H_
 #define COMPONENTS_PRECACHE_CONTENT_PRECACHE_MANAGER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 52 matching lines @@
 class PrecacheManager : public KeyedService,
                         public PrecacheFetcher::PrecacheDelegate,
                         public base::SupportsWeakPtr<PrecacheManager> {
  public:
   typedef base::Callback<void(bool)> PrecacheCompletionCallback;
 
   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);
   ~PrecacheManager() override;
 
   // Returns true if the client is in the experiment group -- that is,
   // precaching is allowed based on user settings, and enabled as part of a
   // field trial or by commandline flag. Virtual for testing.
   virtual bool IsInExperimentGroup() const;
 
   // Returns true if the client is in the control group -- that is, precaching
   // is allowed based on user settings, and the browser is in the control group
   // of the field trial. Virtual for testing.
@@ skipping 51 matching lines @@
     DISALLOWED,
     PENDING
   };
 
   // From KeyedService.
   void Shutdown() override;
 
   // From PrecacheFetcher::PrecacheDelegate.
   void OnDone() override;
 
+  // Registers the precache synthetic field trial for users whom the precache
+  // task was run recently. |last_precache_time| is the last time precache task
+  // was run.
+  void RegisterSyntheticFieldTrial(const base::Time& last_precache_time);
+
   // Callback when fetching unfinished work from storage is done.
   void OnGetUnfinishedWorkDone(
       std::unique_ptr<PrecacheUnfinishedWork> unfinished_work);
 
   // From history::HistoryService::TopHosts.
   void OnHostsReceived(const history::TopHostsList& host_counts);
 
   // Initializes and Starts a PrecacheFetcher with unfinished work.
   void InitializeAndStartFetcher();
 
@@ skipping 44 matching lines @@
   // The PrecacheDatabase for tracking precache metrics. Should only be used on
   // the DB thread.
   std::unique_ptr<PrecacheDatabase> precache_database_;
 
   // Flag indicating whether or not precaching is currently in progress.
   bool is_precaching_;
 
   // Work that hasn't yet finished.
   std::unique_ptr<PrecacheUnfinishedWork> unfinished_work_;
 
+  // Callback to register the synthetic field trial.
+  const base::Callback<void(const base::Time&)>
+      register_synthetic_field_trial_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(PrecacheManager);
 };
 
 }  // namespace precache
 
 #endif  // COMPONENTS_PRECACHE_CONTENT_PRECACHE_MANAGER_H_