The function receives imports and memory, but always calls
SyncInstantiate with null handles. This CL fixes this by passing on the
received values.

R=ahaas@chromium.org

Change-Id: I1ddb617b3d4847db341d97737043cc667f879734
Reviewed-on: https://chromium-review.googlesource.com/753727Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49141}