Transfers ownership of the update area from @window to the caller
of the function. That is, after calling this function, @window will
no longer have an invalid/dirty region; the update area is removed
from @window and handed to you. If a window has no update area,
gdk_window_get_update_area() returns %NULL. You are responsible for
calling cairo_region_destroy() on the returned region if it’s non-%NULL.
Transfers ownership of the update area from @window to the caller of the function. That is, after calling this function, @window will no longer have an invalid/dirty region; the update area is removed from @window and handed to you. If a window has no update area, gdk_window_get_update_area() returns %NULL. You are responsible for calling cairo_region_destroy() on the returned region if it’s non-%NULL.