RemoteImageBufferProxy is not able to wait its own creation confirmation Then didCreateImageBufferBackend cannot be waited correctly
<rdar://problem/110703592>
Pull request: https://github.com/WebKit/WebKit/pull/14914
Committed 265518@main (fd470b96a913): <https://commits.webkit.org/265518@main> Reviewed commits have been landed. Closing PR #14914 and removing active labels.