Post-commit fixes for "stale-while-revalidate..."

I accidentally committed http://crrev.com/455623003 before getting LGTM from
mmenke@. This CL is for additional fixes that he requested.

BUG=348877
TEST=net_unittests

Review URL: https://codereview.chromium.org/665023002

Cr-Commit-Position: refs/heads/master@{#302056}
6 files changed