This allows the back-end to have access to the interface block info
in the link operation, and also allows the interface block info to
have direct access to the post-link Impl information.

BUG=angleproject:2208

Change-Id: Ib2bfb3c9155eee715bd3d29de1c3fdd67b16eed4
Reviewed-on: https://chromium-review.googlesource.com/753521Reviewed-by: Jamie Madill <jmadill@chromium.org>