Auto merge of #9586 - notriddle:details_ui, r=SimonSapin

Details ui

Requires a patch to rust-selectors, and doesn't currently recalculate the styles correctly (which is needed to make actual toggling work correctly).

Still trying to figure out what it takes to get style recalc to do what this needs.

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components/style/selector_impl.rs

@@ -26,6 +26,8 @@ pub trait SelectorImplExt : SelectorImpl + Sized {
 pub enum PseudoElement {
     Before,
     After,
+    DetailsSummary,
+    DetailsContent,
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, HeapSizeOf, Hash)]
@@ -97,12 +99,22 @@ impl SelectorImpl for ServoSelectorImpl {
         Ok(pseudo_class)
     }
 
-    fn parse_pseudo_element(_context: &ParserContext,
+    fn parse_pseudo_element(context: &ParserContext,
                             name: &str) -> Result<PseudoElement, ()> {
         use self::PseudoElement::*;
         let pseudo_element = match_ignore_ascii_case! { name,
             "before" => Before,
             "after" => After,
+            "-servo-details-summary" => if context.in_user_agent_stylesheet {
+                DetailsSummary
+            } else {
+                return Err(())
+            },
+            "-servo-details-content" => if context.in_user_agent_stylesheet {
+                DetailsContent
+            } else {
+                return Err(())
+            },
             _ => return Err(())
         };
 
@@ -122,6 +134,8 @@ impl SelectorImplExt for ServoSelectorImpl {
         where F: FnMut(PseudoElement) {
         fun(PseudoElement::Before);
         fun(PseudoElement::After);
+        fun(PseudoElement::DetailsContent);
+        fun(PseudoElement::DetailsSummary);
     }
 
     #[inline]

components/style/selector_matching.rs

@@ -164,7 +164,6 @@ impl<Impl: SelectorImplExt> Stylist<Impl> {
         if !stylesheet.is_effective_for_device(device) {
             return;
         }
-
         let mut rules_source_order = self.rules_source_order;
 
         // Take apart the StyleRule into individual Rules and insert