MetaWindow: add a public method for checking if the application is responding

Add meta_window_check_alive(), which is a simple wrapper over
meta_display_ping_window(), and takes care of showing the "Application
is not responding dialog" if needed.

https://bugzilla.gnome.org/show_bug.cgi?id=684340

src/core/delete.c

@@ -133,6 +133,18 @@ delete_ping_timeout_func (MetaDisplay *display,
   g_child_watch_add (dialog_pid, dialog_exited, window);
 }
 
+void
+meta_window_check_alive (MetaWindow *window,
+                         guint32     timestamp)
+{
+  meta_display_ping_window (window->display,
+                            window,
+                            timestamp,
+                            delete_ping_reply_func,
+                            delete_ping_timeout_func,
+                            window);
+}
+
 void
 meta_window_delete (MetaWindow  *window,
                     guint32      timestamp)
@@ -156,12 +168,7 @@ meta_window_delete (MetaWindow  *window,
     }
   meta_error_trap_pop (window->display);
 
-  meta_display_ping_window (window->display,
+  meta_window_check_alive (window, timestamp);
-                            window,
-                            timestamp,
-                            delete_ping_reply_func,
-                            delete_ping_timeout_func,
-                            window);
 
   if (window->has_focus)
     {

src/meta/window.h

@@ -190,6 +190,9 @@ void        meta_window_kill               (MetaWindow  *window);
 void        meta_window_focus              (MetaWindow  *window,
                                             guint32      timestamp);
 
+void        meta_window_check_alive        (MetaWindow  *window,
+                                            guint32      timestamp);
+
 void meta_window_begin_grab_op (MetaWindow *window,
                                 MetaGrabOp  op,
                                 gboolean    frame_action,