barrier: Add support for new barrier features in XInput 2.3

XInput 2.3 adds support for "barrier events", which let us know when
a pointer barrier has been hit, and when the pointer has stopped
hitting the barrier, and lets us "release" the barrier, temporarily
letting the pointer pass through the barrier. These features can be
combined to allow for certain pointer gestures, such as "pushing"
against the bottom of the screen, or stopping the pointer on monitor
edges while dragging slowly for increased edge precision.

This commit should allow graceful fallback if servers with
XInput 2.3 aren't supported.

https://bugzilla.gnome.org/show_bug.cgi?id=677215

src/core/display-private.h

@@ -39,6 +39,7 @@
 #include <meta/display.h>
 #include "keybindings-private.h"
 #include <meta/prefs.h>
+#include <meta/barrier.h>
 
 #ifdef HAVE_STARTUP_NOTIFICATION
 #include <libsn/sn.h>
@@ -317,6 +318,12 @@ struct _MetaDisplay
   unsigned int have_damage : 1;
 #define META_DISPLAY_HAS_COMPOSITE(display) ((display)->have_composite)
 #define META_DISPLAY_HAS_DAMAGE(display) ((display)->have_damage)
+#ifdef HAVE_XI23
+  gboolean have_xinput_23 : 1;
+#define META_DISPLAY_HAS_XINPUT_23(display) ((display)->have_xinput_23)
+#else
+#define META_DISPLAY_HAS_XINPUT_23(display) FALSE
+#endif /* HAVE_XI23 */
 };
 
 struct _MetaDisplayClass
@@ -449,4 +456,9 @@ void meta_display_overlay_key_activate (MetaDisplay *display);
 /* In above-tab-keycode.c */
 guint meta_display_get_above_tab_keycode (MetaDisplay *display);
 
+#ifdef HAVE_XI23
+gboolean meta_display_process_barrier_event (MetaDisplay    *display,
+                                             XIBarrierEvent *event);
+#endif /* HAVE_XI23 */
+
 #endif