Implement Element#closest

fixes #4603

- Add definition to the Element.webidl and implementation to element.rs.
- Create inclusive_ancestors helper in NodeHelpers
- Update test expectations

components/script/dom/element.rs

@@ -1120,6 +1120,23 @@ impl<'a> ElementMethods for JSRef<'a, Element> {
             }
         }
     }
+
+    // https://dom.spec.whatwg.org/#dom-element-closest
+    fn Closest(self, selectors: DOMString) -> Fallible<Option<Temporary<Element>>> {
+        let parser_context = ParserContext {
+            origin: StylesheetOrigin::Author,
+        };
+        match style::parse_selector_list_from_str(&parser_context, selectors.as_slice()) {
+            Err(()) => Err(Syntax),
+            Ok(ref selectors) => {
+                let root: JSRef<Node> = NodeCast::from_ref(self);
+                Ok(root.inclusive_ancestors()
+                       .filter_map(ElementCast::to_ref)
+                       .find(|element| matches(selectors, &NodeCast::from_ref(*element), &mut None))
+                       .map(Temporary::from_rooted))
+            }
+        }
+    }
 }
 
 pub fn get_attribute_parts<'a>(name: &'a str) -> (Option<&'a str>, &'a str) {

components/script/dom/node.rs

@@ -397,6 +397,7 @@ impl<'a> Iterator<JSRef<'a, Node>> for QuerySelectorIterator<'a> {
 
 pub trait NodeHelpers<'a> {
     fn ancestors(self) -> AncestorIterator<'a>;
+    fn inclusive_ancestors(self) -> AncestorIterator<'a>;
     fn children(self) -> NodeChildrenIterator<'a>;
     fn rev_children(self) -> ReverseChildrenIterator;
     fn child_elements(self) -> ChildElementIterator<'a>;
@@ -798,6 +799,12 @@ impl<'a> NodeHelpers<'a> for JSRef<'a, Node> {
         }
     }
 
+    fn inclusive_ancestors(self) -> AncestorIterator<'a> {
+        AncestorIterator {
+            current: Some(self.clone())
+        }
+    }
+
     fn owner_doc(self) -> Temporary<Document> {
         self.owner_doc.get().unwrap()
     }

components/script/dom/webidls/Element.webidl

@@ -44,6 +44,9 @@ interface Element : Node {
   boolean hasAttribute(DOMString name);
   boolean hasAttributeNS(DOMString? namespace, DOMString localName);
 
+  [Throws]
+  Element? closest(DOMString selectors);
+
   [Throws]
   boolean matches(DOMString selectors);