Bug 885278 - [SMS] `updateTimeHeaders' is not working properly with FixedHeader feature. r=borja

* always call refresh in updateTimeHeaders
* expose updateHeaderContent and use it in updateTimeHeaders so that the fixed
  header is changed in the same time than the other headers
Merge pull request #10726 from julienw/885278-updatetimeheaders-with-fixedheader

885278 updatetimeheaders with fixedheader