By adding a per test source file namespace, we can avoid a lot of
symbol collisions in jumbo builds.

While we're at it, let's remove some "using" statements that also
cause trouble.

Bug: chromium:746958
Change-Id: I6f8a723e1ba5905888638e0687b23193f3f012ca
Reviewed-on: https://chromium-review.googlesource.com/676803Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Mostyn Bramley-Moore <mostynb@opera.com>
Cr-Commit-Position: refs/heads/master@{#48102}