On the client side message requests can be registered at a desired time

interval. The minimum desired time interval is the interval in which

message requests are made to MessageBus, at url /messagebus/. There is 

currently no handling of the payload response. A MessageRequest called 

ReviewRequestUpdatesMessageRequest was created to handle storing 

relevant data (namely the review request id), which is sent alongside the 

associated message_provider_id as parameters of the request to the 

message bus.
On the server side, requests, identified by their message_provider_id, 

pass their data to the appropriate MessageProvider, which is responsible 

for accumulating messages and writing the data to the payload. Currently, 

a message provider has been created for review request updates, ultimately 

to replace the existing functionality of the ReviewRequestUpdatesView. 

This MessageProvider returns the exact same data as you would expect by 

going to the url /r/<#>/_updates.

A ReviewRequestUpdatesMessageRequest was created and registered to the

client side message bus. The request is received by the server side

message bus, and the request arguments are passed to the

ReviewRequestUpdatesMessageProvider. Any entries registered to the

message request have their payloads properly returned. Not providing an

entry will request all the entries. The data returned, which consists of

two payloads which match up exactly with what url /r/<#>/_updates would

output (message bus is going to replace this, so consistency between the

two is important).