The investigation in #37745 revealed that `Element::create` spends ~39%
of its runtime in `set_custom_element_state`. For built-in, uncustomized
elements this overhead is unnecessary as they are equivalent to being
initialized in the "uncustomized" state. This particular call to
`set_custom_element_state` can't simply be removed as this call also
ensured that the element's DEFINED state is set to 'true', to match
`:defined` selectors, based on the custom element state.
So, introduce a new method that will only set the
`ElementState::DEFINED` flag and call it from `Element::create` when
creating uncustomized, built-ins.
For more information about the peformance improvements, please refer to
[this comment][1].
[1]: https://github.com/servo/servo/issues/37745#issuecomment-3305477287
Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>
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