shell: Make the main window a GtkApplicationWindow

This is a prerequisite of using the new GMenu API. Also move the
check for small screen sizes introduced in commit 22ed5a9fd5, as
GtkApplicationWindows cannot be realized unless their application
property has been set.

https://bugzilla.gnome.org/show_bug.cgi?id=675471

shell/gnome-control-center.c

@@ -1220,6 +1220,21 @@ main_window_configure_cb (GtkWidget *widget,
   return FALSE;
 }
 
+static void
+application_set_cb (GObject    *object,
+                    GParamSpec *pspec,
+                    GnomeControlCenter *self)
+{
+  /* update small screen settings now - to avoid visible resizing, we want
+   * to do it before showing the window, and GtkApplicationWindow cannot be
+   * realized unless its application property has been set */
+  if (gtk_window_get_application (GTK_WINDOW (self->priv->window)))
+    {
+      gtk_widget_realize (self->priv->window);
+      update_small_screen_settings (self);
+    }
+}
+
 static void
 monitors_changed_cb (GdkScreen *screen,
                      GnomeControlCenter *self)
@@ -1266,6 +1281,7 @@ gnome_control_center_init (GnomeControlCenter *self)
   screen = gtk_widget_get_screen (priv->window);
   g_signal_connect (screen, "monitors-changed", G_CALLBACK (monitors_changed_cb), self);
   g_signal_connect (priv->window, "configure-event", G_CALLBACK (main_window_configure_cb), self);
+  g_signal_connect (priv->window, "notify::application", G_CALLBACK (application_set_cb), self);
   g_signal_connect_swapped (priv->window, "delete-event", G_CALLBACK (g_object_unref), self);
   g_signal_connect (priv->window, "key_press_event",
                     G_CALLBACK (window_key_press_event), self);
@@ -1298,10 +1314,6 @@ gnome_control_center_init (GnomeControlCenter *self)
 
   setup_lock (self);
 
-  /* update small screen settings now */
-  gtk_widget_realize (priv->window);
-  update_small_screen_settings (self);
-
   /* store default window title and name */
   priv->default_window_title = g_strdup (gtk_window_get_title (GTK_WINDOW (priv->window)));
   priv->default_window_icon = g_strdup (gtk_window_get_icon_name (GTK_WINDOW (priv->window)));

shell/shell.ui

@@ -2,7 +2,7 @@
 <interface>
   <requires lib="gtk+" version="3.0"/>
   <!-- interface-naming-policy project-wide -->
-  <object class="GtkWindow" id="main-window">
+  <object class="GtkApplicationWindow" id="main-window">
     <property name="title" translatable="yes">System Settings</property>
     <property name="resizable">False</property>
     <property name="icon_name">preferences-desktop</property>