Add isArray overload to handle simple case where input is a readonly array

isArray should keep the output as readonly

src/typings/lib.array-ext.d.ts

@@ -4,6 +4,8 @@
  *--------------------------------------------------------------------------------------------*/
 
 interface ArrayConstructor {
+	isArray<T>(arg: ReadonlyArray<T> | null | undefined): arg is ReadonlyArray<T>;
+	isArray<T>(arg: Array<T> | null | undefined): arg is Array<T>;
 	isArray(arg: any): arg is Array<any>;
 	isArray<T>(arg: any): arg is Array<T>;
 }
\ No newline at end of file

src/vs/workbench/contrib/webview/browser/webviewEditorService.ts

@@ -92,7 +92,7 @@ export function areWebviewInputOptionsEqual(a: WebviewInputOptions, b: WebviewIn
 		&& a.retainContextWhenHidden === b.retainContextWhenHidden
 		&& a.tryRestoreScrollPosition === b.tryRestoreScrollPosition
 		&& (a.localResourceRoots === b.localResourceRoots || (Array.isArray(a.localResourceRoots) && Array.isArray(b.localResourceRoots) && equals(a.localResourceRoots, b.localResourceRoots, (a, b) => a.toString() === b.toString())))
-		&& (a.portMapping === b.portMapping || (Array.isArray(a.portMapping) && Array.isArray(b.portMapping) && equals(a.portMapping, b.portMapping, (a, b) => a.from === b.from && a.to === b.to)));
+		&& (a.portMapping === b.portMapping || (Array.isArray(a.portMapping) && Array.isArray(b.portMapping) && equals(a.portMapping, b.portMapping, (a, b) => a.extensionHostPort === b.extensionHostPort && a.webviewPort === b.webviewPort)));
 }
 
 function canRevive(reviver: WebviewReviver, webview: WebviewEditorInput): boolean {