merge_pr_49810

DOM: Test 'slotchange' event firing during move

See whatwg/dom#1307 (comment).

R=[email protected]

Bug: 40150299
Change-Id: I9529941e05591620da5b3c11635693a15f0ce866
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6111212
Reviewed-by: Noam Rosenthal [email protected]
Commit-Queue: Dominic Farolino [email protected]
Cr-Commit-Position: refs/heads/main@{#1399350}