void registerRequestToDrop(int correlationId) {
    if (requestsToDrop != null) {
      requestsToDrop.add(correlationId);
    }
    // do not remove from correlationIdToOperation here because it will be handled by manager classes when they receive
    // a ResponseInfo.
  }
Register a request to "drop". The current default networking layer drops requests by closing connections.
@param correlationId the correlation ID of the request to drop.
ambry-router/src/main/java/com/github/ambry/router/RequestRegistrationCallback.java