Mark undo-add-property.html flaky.

TBR=luoe@chromium.org

Bug: 978304
Change-Id: Ief1418341e44ed5f67a782be8bfd71f96bbbc47d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1676128
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672079}
1 file changed