If used, the TypeProfileSlot is always added as the first slot and its
index is constant. If other slots are added before the TypeProfileSlot,
this number changes.

BUG=v8:5933

Change-Id: I57bc6bea3c48804af28c2d1dafe6a52bdd7d12e3
Reviewed-on: https://chromium-review.googlesource.com/459511Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Franziska Hinkelmann <franzih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44149}