CefJSDialogHandlerOnBeforeUnloadDialog Method

Called to run a dialog asking the user if they want to leave a page. Return false to use the default dialog implementation. Return true if the application will use a custom dialog or if the callback has been executed immediately. Custom dialogs may be either modal or modeless. If a custom dialog is used the application must execute |callback| once the custom dialog is dismissed.

protected abstract bool OnBeforeUnloadDialog(
	CefBrowser browser,
	string messageText,
	bool isReload,
	CefJSDialogCallback callback
)