Fixed const argument problem from previous commit.

BUG=chromium-os:18816
TEST=ran unittests

Change-Id: Iade85438677475d428a31f872ba55b522b945d26
Reviewed-on: http://gerrit.chromium.org/gerrit/6235
Reviewed-by: David Rochberg <rochberg@chromium.org>
Reviewed-by: Vince Laviano <vlaviano@chromium.org>
Tested-by: Anne Kenyon (Chromium) <annemkenyon@chromium.org>