Add mutation events to "historical" WPT
This set of tests goes along with this spec PR:
Bug: 40268638
Change-Id: I39aafcc0ec1f36704cdc3a263c798c1873333b11
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5803663
Reviewed-by: David Baron dbaron@chromium.org
Auto-Submit: Mason Freed masonf@chromium.org
Commit-Queue: Mason Freed masonf@chromium.org
Cr-Commit-Position: refs/heads/main@{#1345088}