class QueueBufferCallback<RequestType extends AmazonWebServiceRequest,ResultType>
extends java.lang.Object
This class combines the handler we are supposed to call after the request is completed and the
original request object. The reason to hold on to the original request is that we have to provide
it to the async handler on successful completion. Storing the request object here means we don't
have to store it in the classes that do actual work. Those classes tend to forget about the
request objects as soon as the required data was extracted from them.