Auto merge of #7334 - servo:active, r=SimonSapin

Parse :active pseudo-class selector.

This is #7258 with a spec link added in doc-comment.

The pseudo-class is never matched, but this can still help with stylesheets like `a:hover, a:active { color: something }` where failing to parse one pseudo-class makes the entire selector list invalid.

I filed #7333 about actually making it match.

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components/layout/wrapper.rs

@@ -478,6 +478,12 @@ impl<'le> ::selectors::Element for LayoutElement<'le> {
         node.get_focus_state_for_layout()
     }
 
+    #[inline]
+    fn get_active_state(&self) -> bool {
+        let node = NodeCast::from_layout_js(&self.element);
+        node.get_active_state_for_layout()
+    }
+
     #[inline]
     fn get_id(&self) -> Option<Atom> {
         unsafe {