When creating an input element's UA shadow tree, we currently use a ChildChange::Source value that depends on whether the input element itself was parser- or script-inserted. But since UA shadow trees are not exposed to content, and we don't have any dependency on the extra work that inserting using ChildChange::Source::API does, we can use ChildChange::Source::Parser unconditionally. Local testing showed this scored a 0.1% Speedometer 2 improvement.
Created attachment 452261 [details] Patch
Committed r290086 (247441@main): <https://commits.webkit.org/247441@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 452261 [details].
<rdar://problem/89113963>