focusBySelector = function() {
        var element = parentElement[0].querySelector(querySelector);
        return self.byElement(element);
      }
@ngdoc method
@methodOf ui.grid.service:GridUtil.focus
@name bySelector
@description Sets the focus of the document to the given dom element.
@param {(element|angular.element)} parentElement the parent/ancestor of the dom element that you are selecting using the query selector
@param {String} querySelector finds the dom element using the {@link http://www.w3schools.com/jsref/met_document_queryselector.asp querySelector}
@param {boolean} [aSync=false] If true then the selector will be querried inside of a timeout. Otherwise the selector will be querried imidately
then the focus will be called.
@returns {Promise} The `$timeout` promise that will be resolved once focus is set. If another focus is requested before this request is evaluated.
then the promise will fail with the `'canceled'` reason.