Unconditionally setting the JSFunction code to that of the SFI
may skip initializing the feedback vector.

R=leszeks@chromium.org

Bug: v8:7857
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I65d4bf32493be4cade2eaf3d665d44f93e80f809
Reviewed-on: https://chromium-review.googlesource.com/1107618
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53881}