Use the `raise` statement directly.
Switch to using .items() instead of .iteritems(). Python 3 doesn't
have .iteritems() as .items() is a generator, and these are small
enough that the Python 2 overhead should be negligible.
We have to run .keys() through list() in a few places as Python 3
uses a generator and we sometimes want to iterate more than once.
That's why we don't change all .keys() or .items() calls -- most
are in places where generators are fine.
Bug: https://crbug.com/gerrit/10418
Change-Id: I469899d9b77ffd77ccabb831bc4b217407fefe6f