(Bug 41512) Duration of confirmation: 2 -> 3 seconds.

I had some misgivings about bumping the value up by a full second, but
Steven Walling noted that our tests used a 3-second duration. Since
that's the case, if we're serious about relying on data rather than
intuition to make decisions, we should go with what we tested. This does
not, of course, entail shutting off our ears if users find the new
duration obnoxious.

Change-Id: Ia7e7b3ec552ae5d776e718ea8cf4df06774e8d61