[DeviceSync vs] Add FakeCryptAuthMetadataSyncer class

Adds fake implementations of CryptAuthMetadataSyncer and
CryptAuthMetadataSyncerImpl::Factory for use in unit tests.

Bug: 951969
Change-Id: I4824dd609edce07767e921f8a4667d03aa9448d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1712605
Commit-Queue: Josh Nohle <nohle@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680103}
3 files changed