[Sync] Restore previous session if no tabbed windows present

components/sync_sessions/synced_session_tracker.h

 // Copyright 2012 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_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_
 #define COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_
 
 #include <stddef.h>
 
 #include <map>
@@ skipping 78 matching lines @@
 
   // Resets the tracking information for the session specified by |session_tag|.
   // This involves clearing all the windows and tabs from the session, while
   // keeping pointers saved in the synced_window_map_ and synced_tab_map_. Once
   // reset, all calls to PutWindowInSession and PutTabInWindow will denote that
   // the requested windows and tabs are owned and add them back to their
   // session. The next call to CleanupSession(...) will delete those windows and
   // tabs not owned.
   void ResetSessionTracking(const std::string& session_tag);
 
+  // Deletes those windows and tabs associated with |session_tag| that are no
+  // longer owned. See ResetSessionTracking(...)..
+  void CleanupSession(const std::string& session_tag);
+
   // Adds the window with id |window_id| to the session specified by
   // |session_tag|. If none existed for that session, creates one. Similarly, if
   // the session did not exist yet, creates it. Ownership of the SessionWindow
   // remains within the SyncedSessionTracker.
+  // Attempting to add a window to a session multiple times will have no effect.
   void PutWindowInSession(const std::string& session_tag,
                           SessionID::id_type window_id);
 
   // Adds the tab with id |tab_id| to the window |window_id|. If none existed
   // for that session, creates one. Ownership of the SessionTab remains within
   // the SyncedSessionTracker.
   //
   // Note: GetSession(..) must have already been called with |session_tag| to
   // ensure we having mapping information for this session.
   void PutTabInWindow(const std::string& session_tag,
@@ skipping 25 matching lines @@
   // parent this tab. Regardless, when the header is updated then cleanup will
   // remove the actual tab data. However, this method always needs to be called
   // upon foreign tab deletion, otherwise LookupTabNodeIds(...) may return
   // already deleted tab node ids.
   void DeleteForeignTab(const std::string& session_tag, int tab_node_id);
 
   // Deletes the session associated with |session_tag| if it exists.
   // Returns true if the session existed and was deleted, false otherwise.
   bool DeleteForeignSession(const std::string& session_tag);
 
-  // Deletes those windows and tabs associated with |session_tag| that are no
-  // longer owned. See ResetSessionTracking(...)..
-  void CleanupForeignSession(const std::string& session_tag);
-
   // **** Methods specific to the local session. ****
 
   // Set the local session tag. Must be called before any other local session
   // methods are invoked.
   void SetLocalSessionTag(const std::string& local_session_tag);
 
   // Similar to CleanupForeignSession, but also marks any unmapped tabs as free
   // in the tab node pool and fills |deleted_node_ids| with the set of locally
   // free tab nodes to be deleted.
   void CleanupLocalTabs(std::set<int>* deleted_node_ids);
@@ skipping 85 matching lines @@
 
   // Pool of used/available sync nodes associated with local tabs.
   TabNodePool local_tab_pool_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncedSessionTracker);
 };
 
 }  // namespace sync_sessions
 
 #endif  // COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_TRACKER_H_