This makes sure that the Device to DeviceImpl ratio is always 1:1 and
avoids any potential double-deletion or unexpected deletion of
DeviceImpl objects.

BUG=742034

Change-Id: I778068ccd09b7478d3683123456062b94be242a1
Reviewed-on: https://chromium-review.googlesource.com/854627
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>