It will be available on all platforms and it should be off by default for now.
<rdar://problem/101297607>
Pull request: https://github.com/WebKit/WebKit/pull/5499
Committed 255713@main (e0edc782e0e8): <https://commits.webkit.org/255713@main> Reviewed commits have been landed. Closing PR #5499 and removing active labels.