This CL fixes a bug where the receiving instance was updated improperly
in the dispatch table(s) of an imported table.

BUG=chromium:875322
R=mstarzinger@chromium.org

Change-Id: Ib5af238a0847bf332a12863523e897f59f137c1d
Reviewed-on: https://chromium-review.googlesource.com/1196886Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55534}