GitLab

Currently, ProtoDatabase<T> only allows us to have a LevelDB that stores
a single proto type.

In preparation for a single unified proto DB, ProtoDatabase and
ProtoDatabaseImpl have been refactored. Much of ProtoDatabaseImpl's
logic has been moved into ProtoLevelDBWrapper, which contains template
functions instead of being a template class.

ProtoDatabase<T> provides the interface we have today, and we now
have a UniqueProtoDatabase<T> as a thin layer above ProtoDatabase so
that it can manage the unique_ptr to its own LevelDB.
ProtoDatabaseImpl<T> is kept around as an alias for UniqueProtoDatabase
for compatibility, and as a result no ProtoDatabase(Impl) users are
negatively impacted by this change.

The addition of the ProtoLevelDBWrapper provides a convenient place to
record metrics for the various database clients.

Bug: 870813
Change-Id: I6175a3cbea5dd312f09c1d88d5ad80f1f4b26006
Reviewed-on: https://chromium-review.googlesource.com/c/1170093
Commit-Queue: Troy Hildebrandt <thildebr@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598782}