Bug 1499 - clutter_actor_notify_if_geometry_changed causes sync
layout cycles
Whenever clutter_actor_set_{width,height,x,y,size...} is used, extra
synchronous size requests are triggered in
clutter_actor_notify_if_geometry_changed.
If the get_preferred_width() and get_preferred_height() implementations
are particularly costly (e.g. ClutterText) this will result in a performance
impact.
To avoid excessive allocation or requisition cycles we use the
cached values and flags. If we don't have an allocation, we assume
that we need to notify all the properties; if we don't have a size
requisition we notify only width and height; finally, if we do have
a valid allocation we notify only on the changed values.
