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Now called FakeDeviceProvider, existing separately with exposed header, to allow for reuse elsewhere.
Also moved test dependents into 'test_support', out of unittest target. Cleaner + allows for reuse.

Change-Id: I76ca2f2c6de68bb27cf254907e3d7d9a87518ae1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368558
Commit-Queue: Clovis PJ <clovispj@google.com>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804739}