It's similar to to the implicit animation API of ClutterActor and
compatible to deprecated API of ClutterBoxLayout and
ClutterTableLayout.
It adds :use-animations, :easing-mode, :easing-duration and
:easing-delay properties to control animations when allocation of a
child has changed. Layout manager implementers should call
use_animations = clutter_layout_manager_get_easing_state (manager,
&mode,
&duration,
&delay);
from the allocate() virtual function to access these values.
https://bugzilla.gnome.org/show_bug.cgi?id=676827
