GitLab

This is mostly a follow-up to an unintentional behavior change in
https://codereview.chromium.org/2255403002/ .  I decided to treat 0 size as
invalid as well.

BUG=none
TEST=none

Review-Url: https://codereview.chromium.org/2278743002
Cr-Commit-Position: refs/heads/master@{#414215}