components/sync/BUILD.gn: Move device_info tests into own target/build file

This is a preliminary step before moving all of device_info out of
components/sync.

Bug: 947443
Change-Id: I4eb926dd5dae46bffa79a90e2c9eef43bd67866e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583743
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654009}
5 files changed