Optimize SpaceSplitString creation in classAttributeChanged() & partAttributeChanged().
Pull request: https://github.com/WebKit/WebKit/pull/3996
Committed 254139@main (8f13bfc6fbc0): <https://commits.webkit.org/254139@main> Reviewed commits have been landed. Closing PR #3996 and removing active labels.
<rdar://problem/99534595>