Deflake SimpleIndexFileTest.WriteThenLoadIndex.

Deflake SimpleIndexFileTest.WriteThenLoadIndex.

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
Committed: https://crrev.com/67e2ec660017eb124889df3400e1c2298c656e6f
Cr-Commit-Position: refs/heads/master@{#302621}

[gavinp, 2014-11-03 22:03:46]

jkarlin: PTAL.

I wanted this out of the way before proceeding with our stress test deflake. It
initially seemed related, but as you can see it's unrelated. Good to have out of
the way though.

[jkarlin, 2014-11-04 16:17:04]

lgtm

[gavinp, 2014-11-04 16:19:38]

The CQ bit was checked by gavinp@chromium.org

[commit-bot: I haz the power, 2014-11-04 16:20:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/705433002/20001

[commit-bot: I haz the power, 2014-11-04 17:14:32]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-11-04 17:15:05]

Patchset 2 (id:??) landed as
https://crrev.com/67e2ec660017eb124889df3400e1c2298c656e6f
Cr-Commit-Position: refs/heads/master@{#302621}