This reverts dad2857538. That diff had two issues:
- It modifies the JS objects, which means subsequent serialization in
quicksave are 'dirty'.
- It doesn't work with non-extensible objects. That's rather annoying,
and has already caused problems.
It also revert f0faab7a42, which was necessary because of the second
issue.
Fixes#5908
Differential Revision: https://code.wildfiregames.com/D3336
This was SVN commit r24563.