The DMA-BUF renderer already falls back to shared memory if DMA-BUF is not available, which should give similar (or even better) performance.
Pull request: https://github.com/WebKit/WebKit/pull/20869
Committed 271134@main (8b0ce3683045): <https://commits.webkit.org/271134@main> Reviewed commits have been landed. Closing PR #20869 and removing active labels.