Initialize the code table with a valid default (e.g. illegal builtin),
otherwise we're invalidating assumptions when relocating.

Bug: chromium:757217
Change-Id: I77890f1fe0e31534d9844d2e91694df1ec185110
Reviewed-on: https://chromium-review.googlesource.com/630097Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47560}