In the two remaining places that call the {Reset} method, it is already
guaranteed that the {next_instance} and {prev_instance} is undefined.

R=titzer@chromium.org

Change-Id: Iab2e764d88b7ba710c664fea363951fb6f9132e0
Reviewed-on: https://chromium-review.googlesource.com/1113551Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54009}