The code was already careful to use memcpy() here, but then it
added needless casts to wider types that made the compiler think
that it can do 4-byte-aligned accesses when it couldn't.

(It's also a bug that the snapshot got loaded at an unaligned
address, but we can fix both bugs.)

BUG=chromium:729059

Review-Url: https://codereview.chromium.org/2915323002
Cr-Commit-Position: refs/heads/master@{#45698}