The only real implementation is on Cocoa.
Created attachment 388446 [details] Patch
The commit-queue encountered the following flaky tests while processing attachment 388446 [details]: editing/spelling/spellcheck-async-remove-frame.html bug 158401 (authors: morrita@google.com, rniwa@webkit.org, and tony@chromium.org) The commit-queue is continuing to process your patch.
Comment on attachment 388446 [details] Patch Clearing flags on attachment: 388446 Committed r254940: <https://trac.webkit.org/changeset/254940>
All reviewed patches have been landed. Closing bug.
<rdar://problem/58814729>