sync: add garbage collection to SessionsSyncManager

chrome/browser/sync/sessions2/sessions_sync_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 CHROME_BROWSER_SYNC_SESSIONS2_SESSIONS_SYNC_MANAGER_H_
 #define CHROME_BROWSER_SYNC_SESSIONS2_SESSIONS_SYNC_MANAGER_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 127 matching lines @@
   }
 
   // Return the virtual URL of the current tab, even if it's pending.
   static GURL GetCurrentVirtualURL(const SyncedTabDelegate& tab_delegate);
 
   // Return the favicon url of the current tab, even if it's pending.
   static GURL GetCurrentFaviconURL(const SyncedTabDelegate& tab_delegate);
 
   FaviconCache* GetFaviconCache();
 
+  // Triggers garbage collection of stale sessions (as defined by
+  // |stale_session_threshold_days_|). This is called automatically every
+  // time we start up (via AssociateModels) and when new sessions data is
+  // downloaded (sync cycles complete).
+  void DoGarbageCollection();
+
  private:
   // Keep all the links to local tab data in one place. A tab_node_id and tab
   // must be passed at creation. The tab_node_id is not mutable, although
   // all other fields are.
   class TabLink {
    public:
     TabLink(int tab_node_id, const SyncedTabDelegate* tab)
       : tab_node_id_(tab_node_id),
         tab_(tab) {}
 
@@ skipping 164 matching lines @@
   // Unique client tag.
   std::string current_machine_tag_;
 
   // User-visible machine name.
   std::string current_session_name_;
 
   // SyncID for the sync node containing all the window information for this
   // client.
   int local_session_header_node_id_;
 
+  // Number of days without activity after which we consider a session to be
+  // stale and a candidate for garbage collection.
+  size_t stale_session_threshold_days_;
+
   scoped_ptr<LocalSessionEventRouter> local_event_router_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionsSyncManager);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_SESSIONS2_SESSIONS_SYNC_MANAGER_H_