style: Update shadow dom preference.

components/style/gecko/selector_parser.rs

@@ -332,7 +332,7 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
         // NOTE(emilio): Slot assignment and such works per-document, but
         // getting a document around here is not trivial, and it's not worth
         // anyway to handle this in a per-doc basis.
-        unsafe { structs::nsContentUtils_sIsWebComponentsEnabled }
+        unsafe { structs::nsContentUtils_sIsShadowDOMEnabled }
     }
 
     fn pseudo_element_allows_single_colon(name: &str) -> bool {