Implement freezing of updates during resize

Replace the unused meta_compositor_set_updates() with
a reversed-meaning meta_compositor_set_updates_frozen(), and use
it to implement freezing application window updates during
interactive resizing. This avoids drawing new areas of the window
with blank content before the application has a chance to repaint.

https://bugzilla.gnome.org/show_bug.cgi?id=685463

src/core/window-private.h

@@ -343,6 +343,9 @@ struct _MetaWindow
   /* if TRUE, window is attached to its parent */
   guint attached : 1;
 
+  /* if TRUE, we are freezing updates during a resize */
+  guint updates_frozen_for_resize : 1;
+
   /* if non-NULL, the bounds of the window frame */
   cairo_region_t *frame_bounds;
 
@@ -663,4 +666,6 @@ gboolean meta_window_can_tile_side_by_side   (MetaWindow *window);
 
 void meta_window_compute_tile_match (MetaWindow *window);
 
+gboolean meta_window_updates_are_frozen (MetaWindow *window);
+
 #endif