code: function () {
      var deferred = Q.defer();
  
      // store desired capabilities of this session
      this.desiredCapabilities = this.browserData.getDesiredCapabilities(this.browserName, this.config);
      this.browserDefaults = this.browserData.driverDefaults;
      this.browserDefaults.status = this.browserData.getStatusDefaults(this.desiredCapabilities);
  
      // start a browser session
      this._startBrowserSession(deferred, this.desiredCapabilities, this.browserDefaults);
  
      return deferred.promise;
    }
docs: Checks if a webdriver session has already been established,
  if not, create a new one
  
  @method start
  @return {object} promise Driver promise