@Override
                public void handle(IAsyncResult<RateLimitResponse> result) {
                    // No need to handle the response - it's too late to do anything meaningful with the result.
                    // TODO log any error that might have ocurred
                }
Called when everything is done (the last byte is written).  This is used to
record the # of bytes downloaded.
gateway/engine/policies/src/main/java/io/apiman/gateway/engine/policies/TransferQuotaPolicy.java