Created attachment 203653 [details] [review]
app: Request to hide titlebar when maximized

Applications which are designed accordingly can request to have
their titlebar hidden when maximized[0]. Boxes definitively
qualifies, so set the corresponding property on the main window.

[0] https://live.gnome.org/GnomeOS/Design/Whiteboards/WindowStates

ack (btw, the vapi/upstream files modifications should be submitted to vala as well, but someone else took care of it)

Is it planned to support double-click to unmaximize or should we handle it in the app?

Review of attachment 203653 [details] [review]:

ack

Attachment 203653 [details] pushed as 9873520 - app: Request to hide titlebar when maximized

(In reply to comment #2)
> Is it planned to support double-click to unmaximize  [...] ?

It is not as far as I know, but with Metacity/Mutter having moved to GSettings, it should be feasible to implement that behavior. Some random thoughts:

 - using unused space in menu- and toolbars to drag a window is 
   implemented by the Adwaita theme engine (in gnome-themes-standard);
   if we want to implement double-clicks in those areas as well, this
   is where the code should live IMO

 - "double-click to unmaximize" is actually not quite correct - unmaximize
   is just the default value for the "action-double-click-titlebar" setting;
   all UI to change the preference has been removed, but an implementation
   for menubars/toolbars should still follow that setting

 - having gnome-themes-standard depend on gsettings-desktop-schemas should
   be fine, but I think there are efforts to drop the Adwaita theme engine
   (i.e. make the default GTK+ CSS engine powerful enough to handle the
    Adwaita theme) - in that case, gtk itself would depend on g-d-s, which
   sounds more problematic to me