We construct and maintain this LegacyRootInlineBox for the sole purpose of computing some metrics for the line grid feature. We can just compute those things directly.
<rdar://problem/116128479>
Pull request: https://github.com/WebKit/WebKit/pull/18290
Committed 268541@main (f6ffab2867fb): <https://commits.webkit.org/268541@main> Reviewed commits have been landed. Closing PR #18290 and removing active labels.