status/keyboard: Synchronize input source switching with key events

Currently we simply set the gsettings key when activating an input
source. This obviously introduces a time window, between the event that
activates the switch and when the switch is complete, under which key
events are being delivered to applications and interpreted according
to the previous input source.

The patches in bug 696996 introduce a DBus API in g-s-d that allows us
to know when an input source if effectively active. Using that and
freezing keyboard events in the X server until we hear back from g-s-d
we can ensure that events won't be misinterpreted after an input
source switch.

https://bugzilla.gnome.org/show_bug.cgi?id=697007

src/shell-global.c

@@ -1007,6 +1007,13 @@ shell_global_end_modal (ShellGlobal *global,
   meta_plugin_end_modal (global->plugin, timestamp);
 }
 
+void
+shell_global_freeze_keyboard (ShellGlobal *global,
+                              guint32      timestamp)
+{
+  meta_display_freeze_keyboard (global->meta_display, global->stage_xwindow, timestamp);
+}
+
 /* Code to close all file descriptors before we exec; copied from gspawn.c in GLib.
  *
  * Authors: Padraig O'Briain, Matthias Clasen, Lennart Poettering

src/shell-global.h

@@ -44,6 +44,8 @@ gboolean shell_global_begin_modal            (ShellGlobal         *global,
                                               MetaModalOptions    options);
 void     shell_global_end_modal              (ShellGlobal         *global,
                                               guint32              timestamp);
+void     shell_global_freeze_keyboard        (ShellGlobal         *global,
+                                              guint32              timestamp);
 
 typedef enum {
   SHELL_STAGE_INPUT_MODE_NORMAL,