For very large snapshots, calculating the checksum of the snapshot can
take at least 30% of the time to deserialize the snapshot, so add a flag
to skip it.

Change-Id: I8f3418f1d1e9f984e7334ac51096a1a166874722
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3001176
Auto-Submit: Dan Elphick <delphick@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75548}