Depends on D19416. Ref T13110. Ref T13130. See PHI598. When rendering a "Very Large" revision (affecting more than 1,000 files) we currently compute the package/changeset ownership map normally.

This is basically a big list of which packages own which of the files affected by the change. We use it to:

1. Show which packages own each file in the table of contents.
2. Show an "(Owns No Changed Paths)" hint in the reviewers list to help catch out-of-date packages that are no longer relevant.

However, this is expensive to build. We don't render the table of contents at all, so (1) is pointless. The value of (2) is very small on these types of changes, and certainly not worth spending many many seconds computing ownership.

Instead, just skip building out these relationships for very large changes.

Viewed a very large change with package owners; verified it no longer built package map data and rendered the package owners with no "(Owns No Changed Paths)" hints.