code: function setUserRecord(state, userRecord) {
    Object.defineProperty(state, 'userRecord',
      {value: userRecord, writable: true, configurable: true, enumerable: false});
  }
docs: Sets the given user record on the given state that is being tracked for a message.
  @param {MessageState} state - the tracked state to be updated
  @param {UserRecord} userRecord - the user record to link to the state