The default of `enum-variant-name-threshold` is 3, so adding any new
variants will lead to the lint being triggered, reference:
[enum_variant_names](https://rust-lang.github.io/rust-clippy/master/index.html#enum_variant_names).
This PR fix this potential clippy lint warning for facilitate the
addition of new variant in following PR about incremental box tree
update.
Testing: No logic changed, just covered by existing WPT tests
Fixes: None
Signed-off-by: sharpshooter_pt <ibluegalaxy_taoj@163.com>
bda3e23c74