These were added in:
https://chromium.googlesource.com/chromium/src/+/573cef7f96c99540bea732d3425f6fbc8938174f

if (pseudoId == "-webkit-input-placeholder") {
  collectMatchingRulesForList(
      matchRequest.ruleSet->placeholderPseudoRules(), cascadeOrder,
      matchRequest);
}

this means for every element that returns a pseudoId we check the -webkit- prefix which is slow, and also means we've hard coded the details of a specific element and pseudo into the core style engine.

This should be handled through the standard ruleset system like:

matchRequest.ruleSet->shadowPseudoElementRules(pseudoId)

instead. The core style engine shouldn't have any knowledge of specific pseudo elements or input types.