Remove more "using" statements.

Bug: chromium:746958
Change-Id: I2f9c45b1ff1d51fc58b7a702fee046ba3c6a7c17
Reviewed-on: https://chromium-review.googlesource.com/693862Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Mostyn Bramley-Moore <mostynb@vewd.com>
Cr-Commit-Position: refs/heads/master@{#48248}