Add support for CSSNumericValue.toSum(): - https://drafts.css-houdini.org/css-typed-om/#dom-cssnumericvalue-tosum
Pull request: https://github.com/WebKit/WebKit/pull/5480
Committed 255679@main (e3fb2936dcb7): <https://commits.webkit.org/255679@main> Reviewed commits have been landed. Closing PR #5480 and removing active labels.
<rdar://problem/101297441>