GitLab

Adds a ProtoDatabaseProvider(Factory) to provide ProtoDatabases with
the user directory, with ProtoDatabaseProvider as a
BrowserContextKeyedService.

Since ProtoDatabase is just an interface, and the underlying
implementation of it can vary from client to client, a
ProtoDatabaseWrapper that contains a pointer to a ProtoDatabase is
created, also built off ProtoDatabase.

Modifies the Feature Engagement Tracker to use the new provider for
its two databases.

Bug: 870813
Change-Id: I26376a14e8280605b7e3431862e5fe3ad6b9c8db
Reviewed-on: https://chromium-review.googlesource.com/c/1318053Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Commit-Queue: Troy Hildebrandt <thildebr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611878}