When the source actor potentially changes size, that shouldn't
necessarily result in the target actor being redrawn - it should
be like when a child of a container is reallocated due to changes
in its siblings or parent - it should redraw only to the extent
that it is moved and resized. Privately export an internal function
from clutter-actor.c to allow getting this right.
https://bugzilla.gnome.org/show_bug.cgi?id=719367
