GetSystemTimeZones decompile

        public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
        {
            lock (s_internalSyncObject)
            {
                if (!s_allSystemTimeZonesRead)
                {
                    PermissionSet set = new PermissionSet(PermissionState.None);
                    set.AddPermission(new RegistryPermission(RegistryPermissionAccess.Read, @"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones"));
                    set.Assert();
                    using (RegistryKey key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones", RegistryKeyPermissionCheck.Default, RegistryRights.ExecuteKey))
                    {
                        if (key == null)
                        {
                            List<TimeZoneInfo> list;
                            if (s_systemTimeZones != null)
                            {
                                list = new List<TimeZoneInfo>(s_systemTimeZones.Values);
                            }
                            else
                            {
                                list = new List<TimeZoneInfo>();
                            }
                            s_readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(list);
                            s_allSystemTimeZonesRead = true;
                            return s_readOnlySystemTimeZones;
                        }
                        foreach (string str in key.GetSubKeyNames())
                        {
                            TimeZoneInfo info;
                            Exception exception;
                            TryGetTimeZone(str, false, out info, out exception);
                        }
                    }
                    IComparer<TimeZoneInfo> comparer = new TimeZoneInfoComparer();
                    List<TimeZoneInfo> list2 = new List<TimeZoneInfo>(s_systemTimeZones.Values);
                    list2.Sort(comparer);
                    s_readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(list2);
                    s_allSystemTimeZonesRead = true;
                }
                return s_readOnlySystemTimeZones;
            }
        }