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This test was using the wrong mtime as its reference for freshness,
and the index file directory was being created in the wrong order on
creation, which tended to make the first load of an index appear
stale, which was particularly pernicious for a test.

R=jkarlin@chromium.org
BUG=255775

Review URL: https://codereview.chromium.org/705433002

Cr-Commit-Position: refs/heads/master@{#302621}