Track dialog row offline status by timer.

Fixes #6410.

Telegram/SourceFiles/data/data_session.h

@@ -192,6 +192,9 @@ public:
 	void unregisterGroupCall(not_null<GroupCall*> call);
 	GroupCall *groupCall(CallId callId) const;
 
+	void watchForOffline(not_null<UserData*> user, TimeId now = 0);
+	void maybeStopWatchForOffline(not_null<UserData*> user);
+
 	[[nodiscard]] auto invitedToCallUsers(CallId callId) const
 		-> const base::flat_set<not_null<UserData*>> &;
 	void registerInvitedToCallUser(
@@ -717,6 +720,7 @@ private:
 	void setupUserIsContactViewer();
 
 	void checkSelfDestructItems();
+	void checkLocalUsersWentOffline();
 
 	void scheduleNextTTLs();
 	void checkTTLs();
@@ -976,6 +980,9 @@ private:
 	std::vector<WallPaper> _wallpapers;
 	uint64 _wallpapersHash = 0;
 
+	base::flat_map<not_null<UserData*>, TimeId> _watchingForOffline;
+	base::Timer _watchForOfflineTimer;
+
 	rpl::event_stream<WebViewResultSent> _webViewResultSent;
 
 	Groups _groups;