Although most of the top-level sidebar panel subclasses will bail if they're not visible, subviews don't have knowledge of that state and may still layout even when the parent panel is hidden. The only subview of a sidebar should the currently visible panel.
<rdar://problem/49870659>
Created attachment 367367 [details] Patch
Comment on attachment 367367 [details] Patch We should keep an eye on this change, it could introduce regressions.
Comment on attachment 367367 [details] Patch Clearing flags on attachment: 367367 Committed r244268: <https://trac.webkit.org/changeset/244268>
All reviewed patches have been landed. Closing bug.