Daniel van Vugt authored Sep 20, 2018 and Florian Müllner committed Nov 13, 2018

When profiling gnome-shell it was found that one of the main triggers
of `clutter_actor_queue_relayout` during animations was
`clutter_actor_set_margin_internal` continuously setting the same
zero margins. That's obviously pointless but also expensive since it
incurs full stage relayouts and reallocation. So just avoid redundant
margin changes.

Helps to further improve:
GNOME/mutter#233,
GNOME/gnome-shell#349