It's tempting to do this for objects with no internal state, but doing so is unsafe, as it leaks wrappers cross-origin and (likely) leads to UXSS.
Issue 687844 fixed this for window.external, but there are others. Per https://bugs.chromium.org/p/chromium/issues/detail?id=687844#c15, the InputDeviceCapabilities also have this problem.
In a followup, we should make sure that we static_assert that this doesn't happen.
Comment 1 by sigbjo...@opera.com
, Feb 4 2017