ui: always set the frame background to None

This way the xserver never paints the frame background, even if
the client window is destroyed. This allows us to have clean
destroy window animation.

There is no problem with interactive resizing because applications
are using the XSync protocol, so we're not painting unless the
client has redrawn.

https://bugzilla.gnome.org/show_bug.cgi?id=734054

src/ui/ui.c

@@ -331,6 +331,17 @@ meta_ui_get_frame_borders (MetaUI *ui,
                            borders);
 }
 
+static void
+set_background_none (Display *xdisplay,
+                     Window   xwindow)
+{
+  XSetWindowAttributes attrs;
+
+  attrs.background_pixmap = None;
+  XChangeWindowAttributes (xdisplay, xwindow,
+                           CWBackPixmap, &attrs);
+}
+
 Window
 meta_ui_create_frame_window (MetaUI *ui,
                              Display *xdisplay,
@@ -397,6 +408,7 @@ meta_ui_create_frame_window (MetaUI *ui,
 		    &attrs, attributes_mask);
 
   gdk_window_resize (window, width, height);
+  set_background_none (xdisplay, GDK_WINDOW_XID (window));
 
   meta_frames_manage_window (ui->frames, GDK_WINDOW_XID (window), window);
 
@@ -449,16 +461,6 @@ meta_ui_unmap_frame (MetaUI *ui,
     gdk_window_hide (window);
 }
 
-void
-meta_ui_unflicker_frame_bg (MetaUI *ui,
-                            Window  xwindow,
-                            int     target_width,
-                            int     target_height)
-{
-  meta_frames_unflicker_bg (ui->frames, xwindow,
-                            target_width, target_height);
-}
-
 void
 meta_ui_update_frame_style (MetaUI  *ui,
                             Window   xwindow)
@@ -473,13 +475,6 @@ meta_ui_repaint_frame (MetaUI *ui,
   meta_frames_repaint_frame (ui->frames, xwindow);
 }
 
-void
-meta_ui_reset_frame_bg (MetaUI *ui,
-                        Window xwindow)
-{
-  meta_frames_reset_bg (ui->frames, xwindow);
-}
-
 cairo_region_t *
 meta_ui_get_frame_bounds (MetaUI  *ui,
                           Window   xwindow,