Previously, the flow for ticking animations was:
Compositor -> Constellation -> Layout -> Script
However, this means that the compositor <-> layout messages can thrash, meaning layout thread is very rarely idle.
This means that the script thread (which joins on the layout thread during reflow) was unable to execute and run rAF callbacks.
With this change, the flow is now:
Compositor -> Constellation -> Script (when rAF is active).
Compositor -> Constellation -> Layout (when transitions / animations are active and no rAF is present).
This makes rAF based animation *much* smoother.
Source-Repo: https://github.com/servo/servo
Source-Revision: aba500a698584e66975cd93006ca8cf745370f7d
44f92cb1ae