We are currently wrapping the pointer to the instruction start in a
Foreign. The argument buffer, which is also a raw pointer, is passed
directly though.
This CL changes this to also pass the code entry as a raw pointer.

R=mstarzinger@chromium.org

Change-Id: Id7344efa589a5297339ec01c3cfa7688bcc706b3
Reviewed-on: https://chromium-review.googlesource.com/1226970Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55895}