style: Invalidate for CSSOM changes in a more fine-grained way.

Also, for changes in CSS declarations, like changing
cssRules[i].style.color or something, we end up avoiding a lot of the
work we were doing.

This page still trips us in the sense that they add a stylesheet, then
call getBoundingClientRect(), then insert more rules in the stylesheet,
which causes us to rebuild a lot of the cascade data.

We could try to detect appends to the last stylesheet on the list or
something I guess, and avoid rebuilding the cascade data in some cases.

Depends on D85615

Differential Revision: https://phabricator.services.mozilla.com/D85616

components/style/stylist.rs

@@ -13,6 +13,7 @@ use crate::font_metrics::FontMetricsProvider;
 use crate::gecko_bindings::structs::{ServoStyleSetSizes, StyleRuleInclusion};
 use crate::invalidation::element::invalidation_map::InvalidationMap;
 use crate::invalidation::media_queries::{EffectiveMediaQueryResults, ToMediaListKey};
+use crate::invalidation::stylesheets::RuleChangeKind;
 use crate::media_queries::Device;
 use crate::properties::{self, CascadeMode, ComputedValues};
 use crate::properties::{AnimationDeclarations, PropertyDeclarationBlock};
@@ -605,6 +606,18 @@ impl Stylist {
             .remove_stylesheet(Some(&self.device), sheet, guard)
     }
 
+    /// Notify of a change of a given rule.
+    pub fn rule_changed(
+        &mut self,
+        sheet: &StylistSheet,
+        rule: &CssRule,
+        guard: &SharedRwLockReadGuard,
+        change_kind: RuleChangeKind,
+    ) {
+        self.stylesheets
+            .rule_changed(Some(&self.device), sheet, rule, guard, change_kind)
+    }
+
     /// Appends a new stylesheet to the current set.
     #[inline]
     pub fn sheet_count(&self, origin: Origin) -> usize {