Auto merge of #16920 - synlestidae:servo-16705, r=asajeffrey

Implement window.closed

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Implements #16705. window.closed should evaluate to true if BrowsingContext is discarded

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #16705 (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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tests/wpt/metadata/html/browsers/the-window-object/security-window/window-security.html.ini

@@ -339,9 +339,6 @@
   [A SecurityError exception must be thrown when window.stop is accessed from a different origin.]
     expected: FAIL
 
-  [A SecurityError exception should not be thrown when window.closed is accessed from a different origin.]
-    expected: FAIL
-
   [A SecurityError exception should not be thrown when window.length is accessed from a different origin.]
     expected: FAIL
 

tests/wpt/metadata/html/dom/interfaces.html.ini

@@ -4341,9 +4341,6 @@
   [Window interface: attribute toolbar]
     expected: FAIL
 
-  [Window interface: attribute closed]
-    expected: FAIL
-
   [Window interface: operation stop()]
     expected: FAIL
 
@@ -4422,9 +4419,6 @@
   [Window interface: window must inherit property "toolbar" with the proper type (11)]
     expected: FAIL
 
-  [Window interface: window must inherit property "closed" with the proper type (14)]
-    expected: FAIL
-
   [Window interface: window must inherit property "stop" with the proper type (15)]
     expected: FAIL
 

tests/wpt/mozilla/meta/MANIFEST.json

@@ -31734,7 +31734,7 @@
    "testharness"
   ],
   "mozilla/window.html": [
-   "8cfb22096cf713709d6206945ad1bb98a52c4136",
+   "455b488925ce1798c89c2944d4f13dee0cfa32b1",
    "testharness"
   ],
   "mozilla/window_performance.html": [

tests/wpt/mozilla/tests/mozilla/window.html

@@ -9,6 +9,7 @@
 test(function() {
   assert_equals(window, window.self);
   assert_true(window.self instanceof Window, "Should be Window");
+  assert_true(window.closed === false);
 });
 </script>
 </body>