Incremental scope generation

[nzakas]

For ESLint, it would be awesome if we could have incremental scope generation. What I mean is that we are already doing a traversal, but right now we have to do at least two: one for escope and then one for what ESLint is doing. If there was a way to hook escope into using the traversal that ESLint is doing, it would dramatically decrease the running time.

Is this possible?