Auto merge of #12847 - clstl:HTMLDialogElement#close, r=nox

Implements HTMLDialogElement#close

<!-- Please describe your changes on the following line: -->
Implements HTMLDialogElement#close according to [link](https://html.spec.whatwg.org/multipage/#the-dialog-element:dom-dialog-close)

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #12352
- [X] There are tests for these change

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components/script/dom/htmldialogelement.rs

@@ -5,11 +5,14 @@
 use dom::bindings::cell::DOMRefCell;
 use dom::bindings::codegen::Bindings::HTMLDialogElementBinding;
 use dom::bindings::codegen::Bindings::HTMLDialogElementBinding::HTMLDialogElementMethods;
+use dom::bindings::inheritance::Castable;
 use dom::bindings::js::Root;
 use dom::bindings::str::DOMString;
 use dom::document::Document;
+use dom::element::Element;
+use dom::eventtarget::EventTarget;
 use dom::htmlelement::HTMLElement;
-use dom::node::Node;
+use dom::node::{Node, window_from_node};
 use string_cache::Atom;
 
 #[dom_struct]
@@ -56,4 +59,26 @@ impl HTMLDialogElementMethods for HTMLDialogElement {
     fn SetReturnValue(&self, return_value: DOMString) {
         *self.return_value.borrow_mut() = return_value;
     }
+
+    // https://html.spec.whatwg.org/multipage/#dom-dialog-close
+    fn Close(&self, return_value: Option<DOMString>) {
+        let element = self.upcast::<Element>();
+        let target = self.upcast::<EventTarget>();
+        let win = window_from_node(self);
+
+        // Step 1 & 2
+        if element.remove_attribute(&ns!(), &atom!("open")).is_none() {
+            return;
+        }
+
+        // Step 3
+        if let Some(new_value) = return_value {
+            *self.return_value.borrow_mut() = new_value;
+        }
+
+        // TODO: Step 4 implement pending dialog stack removal
+
+        // Step 5
+        win.dom_manipulation_task_source().queue_simple_event(target, atom!("close"), win.r());
+    }
 }

components/script/dom/webidls/HTMLDialogElement.webidl

@@ -8,5 +8,5 @@ interface HTMLDialogElement : HTMLElement {
   attribute DOMString returnValue;
   //void show(optional (MouseEvent or Element) anchor);
   //void showModal(optional (MouseEvent or Element) anchor);
-  //void close(optional DOMString returnValue);
+  void close(optional DOMString returnValue);
 };