- Return true or false, not undefined
- Check that unregister token is an object

Bug: v8:8179
Change-Id: I1a4ff7730158dba16efb552fb2f4892c8d31412c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1653120Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62135}