[Chromeshine] Switch to single ProtoDatabase for UsageStatsDatabase.

Necessary due to ~30kB binary size increase that resulted from the addition of 3 new leveldb_proto::ProtoDatabase instances in UsageStatsDatabase.

Bug: 921112
Change-Id: Ie5ad871449260c92ce08fe92bfde65273eb31218
Reviewed-on: https://chromium-review.googlesource.com/c/1407432
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Reviewed-by: Patrick Noland <pnoland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622155}
3 files changed