Avoid copying ListHashSet inside RenderLayer::topLayerRenderLayers().
Pull request: https://github.com/WebKit/WebKit/pull/3493
Committed 253614@main (bb5e3d4d63fb): <https://commits.webkit.org/253614@main> Reviewed commits have been landed. Closing PR #3493 and removing active labels.
<rdar://problem/98909681>