RateChatCell appends a row to cell_rating for every click; thumbs-down also upserts a user_thumbs_down thread_warning.

A generic empty message that you can re-use to avoid defining duplicated empty messages in your APIs. A typical example is to use it as the request or the response type of an API method. For instance:

 service Foo {
   rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);
 }