Bug: 26925668 Change-Id: Ic56460926bd62ac41e64f4d37f52d962976ca644
First of several change lists: 1. Add in the new proto (this CL) 2. Migrate the existing code over to the proto. 3. Remove MetricsConstants once it is unused. Bug: 26442178 Change-Id: Ic24829246af8ec5b202e39a85960aac5cf336c33