Introduced a CHECK instead and details about the invariant it relies on.

R=neis@chromium.org, rmcilroy@chromium.org

Change-Id: I568fc6d737c6bf70bd7aabf47df22651e3fcf8fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1517882Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60234}