code: function parseIpcMessage(message, cb) {
    var requestId;
    if (message._requestId == null) { // eslint-disable-line eqeqeq
      throw new Error('Invalid message: ' + JSON.stringify(message));
    }
    requestId = message._requestId;
    delete message._requestId;
    return cb(+requestId, message);
  }
docs: Callback that handles the parsed message object.
  @callback procMessage
  @param {string} requestId - ID of the message.
  @param {Object} message - The message object.
   
  Normalize an IPC message.
  @param {Object} message - IPC message.
  @param {procMessage} cb - Callback function that is called.
  @returns {any} Something that was returned by `cb`.