[x11] Send a valid timestamp in TakeFocus messages
Kwin sends out undated WM_TAKE_FOCUS client messages. Gtk based applications such as Firefox react to these by handing focus to one of their subwindows using XSetInputFocus(), and pass on the null time field that they received in the client message to XSetInputFocus().
If for whatever reason the application (firefox) is slow to process the event, it might issue that XSetInputFocus() message at a time when it has already lost focus to the next application. This results in Firefox stealing back the focus from the next application. Normally, such an occurrence would not happen, as the server could tell by the time field that the message is stale.
Until 2016 (e73e331f) kwin used to send a valid timestamp, but this got deliberately broken to appease some Java Applications which were "extremely picky" and would refuse focus.
This was based on the assumption that no other toolkit used the timestamp from take focus events which is now proven to be false.
ICCCM document states:
Windows with the atom WM_TAKE_FOCUS in their WM_PROTOCOLS property may receive a ClientMessage event from the window manager (as described in section 4.2.8) with WM_TAKE_FOCUS in its data[0] field and a valid timestamp (i.e. not CurrentTime ) in its data[1] field."