Adopt more smart pointers in Source/WebCore/dom/messageports.
Pull request: https://github.com/WebKit/WebKit/pull/19681
Committed 269911@main (72f8ce4e3746): <https://commits.webkit.org/269911@main> Reviewed commits have been landed. Closing PR #19681 and removing active labels.
<rdar://problem/117656033>