Avoid repeated :has() child-list scheduling when pending data already
covers every concrete feature bucket used by :has() selectors in a style
scope. Featureless-sensitive scopes record child-list mutations
conservatively instead.
That conservative path avoids scanning mutation subtrees for concrete
features when invalidation cannot rely on them anyway. When loading
the Intel ISA PDF in pdf.js, instrumented subtree feature-collection
visits at about 40k style invalidations dropped from around 71k to 1.6k,
saving ~650ms of main thread time on my Linux machine. :^)
Collect concrete features from pending :has() mutations and use them to
avoid re-invalidating non-subject :has() anchors whose matching rules
cannot be affected by the mutation.
Keep conservative behavior for shadow-boundary fanout, structural
sibling changes, and selectors whose relevant features cannot be proven.
For sibling-combinator relative selectors, avoid marking an anchor as
handled until it is actually invalidated, and make the sibling scan
respect anchors skipped by the feature filter for the same mutation.
Keep StyleScope responsible for storing pending :has() mutation state,
but move the invalidation walk and scheduling helpers into
CSS::Invalidation::HasMutationInvalidator. This keeps the style scope
from owning the :has() invalidation algorithm directly and gives later
changes a narrower place to optimize.
Document.cpp still flushed pending :has() invalidation by walking the
document and shadow-root style scopes directly. Move that CSS-specific
flush into CSS::Invalidation::HasMutationInvalidator.
Document continues to own the flag that says a :has() flush is needed.
The helper now owns the style-scope work needed to invalidate elements
affected by pending :has() mutations.
Element exposed a small method that encoded how :has()-affected elements
are marked dirty. Move that policy into CSS::Invalidation alongside the
rest of the :has() mutation invalidation helpers.
This keeps Element focused on DOM state while preserving the existing
subject and non-subject :has() invalidation behavior.
Node.cpp still contained the policy for deciding when a DOM mutation
should schedule pending :has() invalidation work. Move that into
CSS::Invalidation::HasMutationInvalidator, next to the mutation feature
collector it depends on.
This keeps DOM mutation code focused on reporting that a mutation
happened, while CSS invalidation code owns the selector-specific checks
for :has() metadata and sibling-combinator sensitivity.
