code: function commonEventHandler(event, arg) {
      // NOTE: send from renderer process always.
      var successEventName = getSuccessEventName(arg.eventName, arg.id);
      var failureEventName = getFailureEventName(arg.eventName, arg.id);
  
      var onSuccess = function(result) {
        // send success to ipc for renderer process.
        event.sender.send(COMMON_SUCCESS_EVENT_NAME, {
          data: result,
          eventName: arg.eventName,
          id: arg.id
        });
        cee.removeListener(successEventName, onSuccess);
        cee.removeListener(failureEventName, onFailure);
      };
      var onFailure = function(result) {
        // send failure to ipc for renderer process.
        event.sender.send(COMMON_FAILURE_EVENT_NAME, {
          data: result,
          eventName: arg.eventName,
          id: arg.id
        });
        cee.removeListener(successEventName, onSuccess);
        cee.removeListener(failureEventName, onFailure);
      };
  
      // add listener to common event emitter for main process.
      cee.on(successEventName, onSuccess);
      cee.on(failureEventName, onFailure);
  
      // emit to common event emitter for main process.
      cee.emit(arg.eventName, arg.id, arg.data, event);
    }
docs: common event handler for ipc.
  
  @private
  @param {Event} event event object.
  @param {Object} arg argument object.