input: Add notify_touch_cancel()

We already have notify_touch(), notify_touch_frame().  We need
notify_touch_cancel() to implement touch in the weston wayland backend
properly.

Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>

src/compositor.h

@@ -1158,6 +1158,9 @@ notify_touch(struct weston_seat *seat, uint32_t time, int touch_id,
 void
 notify_touch_frame(struct weston_seat *seat);
 
+void
+notify_touch_cancel(struct weston_seat *seat);
+
 void
 weston_layer_entry_insert(struct weston_layer_entry *list,
 			  struct weston_layer_entry *entry);

src/input.c

@@ -1807,6 +1807,15 @@ notify_touch_frame(struct weston_seat *seat)
 	grab->interface->frame(grab);
 }
 
+WL_EXPORT void
+notify_touch_cancel(struct weston_seat *seat)
+{
+	struct weston_touch *touch = weston_seat_get_touch(seat);
+	struct weston_touch_grab *grab = touch->grab;
+
+	grab->interface->cancel(grab);
+}
+
 static int
 pointer_cursor_surface_get_label(struct weston_surface *surface,
 				 char *buf, size_t len)