Cache common protobuf requests.
Cache common protobuf requests.

Caching common protobuf requests (which have no params) instead of creating
and serializing them again and again (thanks Jonas!).

Change-Id: Id39098c8276cfa95b11fc288ed9d3a46375c7974

google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian