Because SizeFor only returns aligned values, when we check values
returned there against kMaxSize, they can be larger if they were
rounded up.

It wasn't possible to write a test for the 2-byte version that didn't
regularly OOM.

Bug: chromium:752764
Change-Id: Id2f387449e0fafe633a2fde1ac728be31487f62d
Reviewed-on: https://chromium-review.googlesource.com/607935Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47252}