style: Support matching :-moz-browser-frame and :-moz-table-border-nonzero against snapshots.

components/style/servo/selector_parser.rs

@@ -268,6 +268,12 @@ impl NonTSPseudoClass {
     pub fn needs_cache_revalidation(&self) -> bool {
         self.state_flag().is_empty()
     }
+
+    /// Returns true if the evaluation of the pseudo-class depends on the
+    /// element's attributes.
+    pub fn is_attr_based(&self) -> bool {
+        false
+    }
 }
 
 /// The abstract struct we implement the selector parser implementation on top