Removes the nullable attribute from window.parent (#1089)

* Remvoes the nullable attribute from parent

* Adds a comment about why it's not null

* Expand copy

* Update inputfiles/comments.json

Co-authored-by: Kagami Sascha Rosylight <saschanaz@outlook.com>

* Fix baselines

Co-authored-by: Kagami Sascha Rosylight <saschanaz@outlook.com>

Author: Orta Therox

baselines/dom.generated.d.ts

@@ -17230,7 +17230,12 @@ interface Window extends EventTarget, AnimationFrameProvider, GlobalEventHandler
     readonly pageXOffset: number;
     /** @deprecated This is a legacy alias of `scrollY`. */
     readonly pageYOffset: number;
-    readonly parent: WindowProxy | null;
+    /**
+     * Refers to either the parent WindowProxy, or itself.
+     *
+     * It can rarely be null e.g. for contentWindow of an iframe that is already removed from the parent.
+     */
+    readonly parent: WindowProxy;
     /**
      * Returns true if the personal bar is visible; otherwise, returns false.
      */
@@ -18294,7 +18299,12 @@ declare var outerWidth: number;
 declare var pageXOffset: number;
 /** @deprecated This is a legacy alias of `scrollY`. */
 declare var pageYOffset: number;
-declare var parent: WindowProxy | null;
+/**
+ * Refers to either the parent WindowProxy, or itself.
+ *
+ * It can rarely be null e.g. for contentWindow of an iframe that is already removed from the parent.
+ */
+declare var parent: WindowProxy;
 /**
  * Returns true if the personal bar is visible; otherwise, returns false.
  */

inputfiles/comments.json

@@ -1796,6 +1796,15 @@
                         }
                     }
                 }
+            },
+            "Window": {
+                "properties": {
+                    "property": {
+                        "parent": {
+                            "comment" : "/**\n * Refers to either the parent WindowProxy, or itself.\n *\n * It can rarely be null e.g. for contentWindow of an iframe that is already removed from the parent.\n */"
+                        }
+                    }
+                }
             }
         }
     }

inputfiles/overridingTypes.jsonc

@@ -500,6 +500,9 @@
                         },
                         "window": {
                             "overrideType": "Window & typeof globalThis"
+                        },
+                        "parent": {
+                            "nullable": false
                         }
                     }
                 },