This addresses follow-up comments to https://crrev.com/c/1354887/.

Use DCHECKs instead of CHECKs and make the branch order consistent
across architectures.

Bug: v8:7777
Change-Id: I5c3f8f5ac97b55fa80662bc211aff7833ff12bfa
Reviewed-on: https://chromium-review.googlesource.com/c/1362912
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58063}