Nashorn's optimistic typing feature from the Open JDK 9 repository needs to be backported to the 8u repository.

Since the implementation in the 9 repo is contained across many changesets (not even linearizable - there are merges), it'd be extremely unfeasible to backport them one by one, replaying the merges (some of which took several days to resolve conflicts). Rather, a single backport changeset should be prepared that will be the diff between current 9 and 8 tip (modulo version number strings), as there is nothing in Nashorn's 9 repo that should not go (or is not already present) in the 8 repo.