Primary change is the removal of a CheckValue that is
unnecessary because we only care about the map and there's
already a CheckMaps.

Secondary change is a minor refactoring for clarity.

Change-Id: I96abd1bc2b38919fd08daa1c688298f8807a0fe7
Reviewed-on: https://chromium-review.googlesource.com/c/1326026Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57395}