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* Moves PhoneHubManager to PhoneHubManagerImpl.
* PhoneHubManagerImpl and FakePhoneHubManager are now derived classes.
* FakePhoneHubManager will be used by the debug UI to be added in a
  later CL.

Bug: 1106937
Change-Id: Iee1c6b4b787f36a7a50eb83fcd1ae1e626f7eecc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375740Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Regan Hsu <hsuregan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801852}