RemoteImageBufferProxy waits flushes in a dedicated a work queue This is a bit redundant, the waits can happen just when needed. From bug 256073
<rdar://problem/109257081>
Pull request: https://github.com/WebKit/WebKit/pull/13803
Committed 264240@main (2fed4020085c): <https://commits.webkit.org/264240@main> Reviewed commits have been landed. Closing PR #13803 and removing active labels.