Use Vector::uncheckedAppend() less in WebCore and replace with faster alternatives now that uncheckedAppend() has become an alias for append().
Pull request: https://github.com/WebKit/WebKit/pull/18744
Committed 269027@main (4a0b13037eb2): <https://commits.webkit.org/269027@main> Reviewed commits have been landed. Closing PR #18744 and removing active labels.
<rdar://problem/116607067>