Traces show that that we mark the scrollbar layers as needing repaint, and hit GraphicsLayerCA::platformCALayerPaintContents() for them, on every scroll. If these are layers for native scrollbars, we don't paint them in the web process at all (the NSScrollerImps only live in the UI Process), so we shouldn't need to dirty the scrollbar layers.
<rdar://problem/109184266>
Pull request: https://github.com/WebKit/WebKit/pull/13840
Committed 264094@main (d19192443a84): <https://commits.webkit.org/264094@main> Reviewed commits have been landed. Closing PR #13840 and removing active labels.