The current code couldn't handle some uses of interface blocks,
such as blocks with instance names.

BUG=angle:466

Change-Id: I0a3746f277af0538cede30232532c6788412da1c
Reviewed-on: https://chromium-review.googlesource.com/213502Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Nicolas Capens <capn@chromium.org>