Cleanup of how -enableDesktopUserAgent uses NavigationManager utility.

ios/chrome/browser/web/navigation_manager_util.h

Index: ios/chrome/browser/web/navigation_manager_util.h
diff --git a/ios/chrome/browser/web/navigation_manager_util.h b/ios/chrome/browser/web/navigation_manager_util.h
index 24ec5b38c296fe3380892ad4dfbabae689f2d16e..20f1cef6507fa42ad6d209bf3c2fc8c859e43c5b 100644
--- a/ios/chrome/browser/web/navigation_manager_util.h
+++ b/ios/chrome/browser/web/navigation_manager_util.h
@@ -11,8 +11,8 @@
 // Utility functions built on web::NavigationManager public API.
 
 // Returns the most recent navigation item that is not the result of an HTTP
-// Redirect. Returns nullptr if |nav_manager| is empty or the first item if
-// all items are redirects.
+// Redirect. Returns nullptr if |nav_manager| is nullptr or is empty.
+// If all items are redirects, the first item is returned.
 web::NavigationItem* GetLastNonRedirectedItem(
     web::NavigationManager* nav_manager);