Clean up repeated code in picture pile unittest

Clean up repeated code in picture pile unittest

This is just a prefactoring to make it easier to write another picture
pile test for the given bug.

BUG=353346
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=257766

[danakj, 2014-03-18 17:14:04]

LGTM

[enne (OOO), 2014-03-18 17:16:17]

The CQ bit was checked by enne@chromium.org

[commit-bot: I haz the power, 2014-03-18 17:35:03]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/enne@chromium.org/198833004/1

[commit-bot: I haz the power, 2014-03-18 21:26:50]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-18 21:26:52]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[enne (OOO), 2014-03-18 21:27:32]

The CQ bit was checked by enne@chromium.org

[commit-bot: I haz the power, 2014-03-18 21:29:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/enne@chromium.org/198833004/1

[commit-bot: I haz the power, 2014-03-18 21:37:46]

Change committed as 257766