style: Simplify selector flags setup even more

In my investigation for bug 1766439, I am digging into why selector
matching regressed.

It doesn't help that the selector-matching code is instantiated a
gazillion times (so there's a ton of copies of the relevant functions).

This was needed in the past because we had different ways of setting the
selector flags on elements, but I unified that recently and now we only
need to either set them or not. That is the kind of thing that
MatchingContext is really good for, so pass that instead on
MatchingContext creation.

Differential Revision: https://phabricator.services.mozilla.com/D145428

components/style/sharing/mod.rs

@@ -75,7 +75,7 @@ use crate::stylist::Stylist;
 use crate::values::AtomIdent;
 use atomic_refcell::{AtomicRefCell, AtomicRefMut};
 use owning_ref::OwningHandle;
-use selectors::matching::{ElementSelectorFlags, VisitedHandlingMode};
+use selectors::matching::{VisitedHandlingMode, NeedsSelectorFlags};
 use selectors::NthIndexCache;
 use servo_arc::Arc;
 use smallbitvec::SmallBitVec;
@@ -222,18 +222,17 @@ impl ValidationData {
     /// Computes the revalidation results if needed, and returns it.
     /// Inline so we know at compile time what bloom_known_valid is.
     #[inline]
-    fn revalidation_match_results<E, F>(
+    fn revalidation_match_results<E>(
         &mut self,
         element: E,
         stylist: &Stylist,
         bloom: &StyleBloom<E>,
         nth_index_cache: &mut NthIndexCache,
         bloom_known_valid: bool,
-        flags_setter: &mut F,
+        needs_selector_flags: NeedsSelectorFlags,
     ) -> &SmallBitVec
     where
         E: TElement,
-        F: FnMut(&E, ElementSelectorFlags),
     {
         self.revalidation_match_results.get_or_insert_with(|| {
             // The bloom filter may already be set up for our element.
@@ -256,7 +255,7 @@ impl ValidationData {
                 element,
                 bloom_to_use,
                 nth_index_cache,
-                flags_setter,
+                needs_selector_flags,
             )
         })
     }
@@ -326,7 +325,9 @@ impl<E: TElement> StyleSharingCandidate<E> {
             bloom,
             nth_index_cache,
             /* bloom_known_valid = */ false,
-            &mut |_, _| {},
+            // The candidate must already have the right bits already, if
+            // needed.
+            NeedsSelectorFlags::No,
         )
     }
 }
@@ -399,17 +400,13 @@ impl<E: TElement> StyleSharingTarget<E> {
         // The style sharing cache will get a hit for the second span. When the
         // child span is subsequently removed from the DOM, missing selector
         // flags would cause us to miss the restyle on the second span.
-        let mut set_selector_flags = |el: &E, flags: ElementSelectorFlags| {
-            el.apply_selector_flags(flags);
-        };
-
         self.validation_data.revalidation_match_results(
             self.element,
             stylist,
             bloom,
             nth_index_cache,
             /* bloom_known_valid = */ true,
-            &mut set_selector_flags,
+            NeedsSelectorFlags::Yes,
         )
     }