app/modules/main/templates/cells/generateCellValue.html
<span ng-if="!headerRowData.columnFilter.isEnabled">
{{headerRowData.columnName}}
</span>
<span ng-if="headerRowData.columnFilter.isEnabled"
class="filter-select"
ng-class="{'is-active': headerRowData.columnFilter.filtersApplied.length}">
{{headerRowData.columnName}}
<ng-md-icon icon="arrow_drop_down" size="24"></ng-md-icon>
</span>