The snapshot's Checksum function internally uses adler32, which
appears to be significantly faster than base::hash_range and almost as
fast as doing nothing at all.

Test times, measured with

$ time tools/run-tests.py --outdir out/release-with-dchecks/
--exit-after-n-failures=1 --quickcheck

base::hash_range: 1m35s
adler32: 1m15s
nop: 1m13s

Bug: chromium:1047818
Change-Id: I8def62f6276a3d06d06911abf5368f59331245ea
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2187492Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67649}