Auto merge of #22933 - pngai:implement-returnValue-attribute, r=jdm

Implement historical returnValue attribute for Event interface

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Implementation of `returnValue` attribute for Event interface.

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- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #22881 (GitHub issue number if applicable)

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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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components/script/dom/event.rs

@@ -297,6 +297,18 @@ impl EventMethods for Event {
         self.cancelable.get()
     }
 
+    // https://dom.spec.whatwg.org/#dom-event-returnvalue
+    fn ReturnValue(&self) -> bool {
+        self.canceled.get() == EventDefault::Allowed
+    }
+
+    // https://dom.spec.whatwg.org/#dom-event-returnvalue
+    fn SetReturnValue(&self, val: bool) {
+        if !val {
+            self.PreventDefault();
+        }
+    }
+
     // https://dom.spec.whatwg.org/#dom-event-timestamp
     fn TimeStamp(&self) -> u64 {
         self.timestamp

components/script/dom/webidls/Event.webidl

@@ -26,6 +26,7 @@ interface Event {
   readonly attribute boolean bubbles;
   [Pure]
   readonly attribute boolean cancelable;
+  attribute boolean returnValue;  // historical
   void preventDefault();
   [Pure]
   readonly attribute boolean defaultPrevented;