adler32 is strictly faster than the old checksum - see this doc:
https://docs.google.com/document/d/1fFhuShavlUwf0FqTc-6L3XLYbAVe0DhpmHSv4oenZL8/edit?pli=1#heading=h.ojvfq6akbz5f

adler32 also no longer requires alignment to be maintained.

Bug: chromium:833361
Change-Id: I3dbfa699b712aa908c87e6f8261756a4a1209df4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1925562
Commit-Queue: Sam Maier <smaier@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65160}