code: function(auditRuleName) {
          if (!(auditRuleName in this.rules_))
              return null;
          if (!('config' in this.rules_[auditRuleName]))
              return null;
          return this.rules_[auditRuleName].config;
      }
docs: Gets the user-specified configuration for the given audit rule.
  @param {string} auditRuleName
  @return {Object?} The configuration object for the given audit rule.