Add experiment to disable loading of background tabs during session restore.

chrome/browser/sessions/session_restore_stats_collector.h

 // Copyright 2015 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 CHROME_BROWSER_SESSIONS_SESSION_RESTORE_STATS_COLLECTOR_H_
 #define CHROME_BROWSER_SESSIONS_SESSION_RESTORE_STATS_COLLECTOR_H_
 
 #include <set>
 
 #include "base/callback_list.h"
@@ skipping 10 matching lines @@
 // SessionRestoreStatsCollector observes SessionRestore events ands records UMA
 // accordingly.
 class SessionRestoreStatsCollector
     : public content::NotificationObserver,
       public base::RefCounted<SessionRestoreStatsCollector> {
  public:
   // Called to start tracking tabs. If a restore is already occuring, the tabs
   // are added to the existing list of tracked tabs.
   static void TrackTabs(
       const std::vector<SessionRestoreDelegate::RestoredTab>& tabs,
-      const base::TimeTicks& restore_started);
+      const base::TimeTicks& restore_started,
+      bool active_only);
 
  private:
   friend class base::RefCounted<SessionRestoreStatsCollector>;
 
   using RenderWidgetHostSet = std::set<content::RenderWidgetHost*>;
 
-  explicit SessionRestoreStatsCollector(const base::TimeTicks& restore_started);
+  explicit SessionRestoreStatsCollector(const base::TimeTicks& restore_started,
+                                        bool active_only);
   ~SessionRestoreStatsCollector() override;
 
   // NotificationObserver method.
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // Adds new tabs to the list of tracked tabs.
   void AddTabs(const std::vector<SessionRestoreDelegate::RestoredTab>& tabs);
 
@@ skipping 27 matching lines @@
 
   // The number of tabs that have been restored.
   int tab_count_;
 
   // Max number of tabs that were loaded in parallel (for metrics).
   size_t max_parallel_tab_loads_;
 
   // Notification registrar.
   content::NotificationRegistrar registrar_;
 
+  // Are we only restoring active tabs?
+  bool active_only_;
+
   // To keep the collector alive as long as needed.
   scoped_refptr<SessionRestoreStatsCollector> this_retainer_;
 
   // The shared SessionRestoreNotifier instance for all SessionRestores running
   // at this time.
   static SessionRestoreStatsCollector* shared_collector_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionRestoreStatsCollector);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_SESSION_RESTORE_STATS_COLLECTOR_H_