[Sync] Restore previous session if no tabbed windows present

components/sync_sessions/synced_session_tracker.h

Index: components/sync_sessions/synced_session_tracker.h
diff --git a/components/sync_sessions/synced_session_tracker.h b/components/sync_sessions/synced_session_tracker.h
index 506d3d0cbeecb802b6aa39f9fc27f2d337de599f..f0324796f48eab6679a5f3789e0ebd206995287d 100644
--- a/components/sync_sessions/synced_session_tracker.h
+++ b/components/sync_sessions/synced_session_tracker.h
@@ -96,10 +96,15 @@ class SyncedSessionTracker {
   // 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);
 
@@ -145,10 +150,6 @@ class SyncedSessionTracker {
   // 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