We currently rely on timers to trigger style updates/render tree updates, and this is necessary to trigger unfreezing the layer tree (via visually empty threshold). Ideally the style system would not have any of its own timers; it would just schedule rendering updates. However, TiledCoreAnimationDrawingArea::triggerRenderingUpdate() just bails if the layer tree is frozen.
We need to somehow harmonize layer tree freezing with rendering updates.
See rdar://75362363 and http://trac.webkit.org/changeset/272300/webkit
(In reply to Simon Fraser (smfr) from comment #1)
> See rdar://75362363 and http://trac.webkit.org/changeset/272300/webkit
... and https://trac.webkit.org/changeset/280112/webkit