Change return type of window.open to Window | null (#18132)

Author: heejongahn

baselines/dom.generated.d.ts

@@ -13277,7 +13277,7 @@ interface Window extends EventTarget, WindowTimers, WindowSessionStorage, Window
     moveBy(x?: number, y?: number): void;
     moveTo(x?: number, y?: number): void;
     msWriteProfilerMark(profilerMarkName: string): void;
-    open(url?: string, target?: string, features?: string, replace?: boolean): Window;
+    open(url?: string, target?: string, features?: string, replace?: boolean): Window | null;
     postMessage(message: any, targetOrigin: string, transfer?: any[]): void;
     print(): void;
     prompt(message?: string, _default?: string): string | null;
@@ -14677,7 +14677,7 @@ declare function matchMedia(mediaQuery: string): MediaQueryList;
 declare function moveBy(x?: number, y?: number): void;
 declare function moveTo(x?: number, y?: number): void;
 declare function msWriteProfilerMark(profilerMarkName: string): void;
-declare function open(url?: string, target?: string, features?: string, replace?: boolean): Window;
+declare function open(url?: string, target?: string, features?: string, replace?: boolean): Window | null;
 declare function postMessage(message: any, targetOrigin: string, transfer?: any[]): void;
 declare function print(): void;
 declare function prompt(message?: string, _default?: string): string | null;

inputfiles/overridingTypes.json

@@ -615,7 +615,7 @@
         "kind": "method",
         "interface": "Window",
         "name": "open",
-        "signatures": ["open(url?: string, target?: string, features?: string, replace?: boolean): Window"]
+        "signatures": ["open(url?: string, target?: string, features?: string, replace?: boolean): Window | null"]
     },
     {
         "kind": "method",