As a prerequisite, you have to consume the url contract in the CHIP definition XML.
The url property is then available in the CHIP API object. It provides the method chip.url.toAbsoluteUrl() to convert a relative URL into an absolute URL.
var oChipApi = this.getView().getViewData().chip, sImageUrl = oChipApi.url.toAbsoluteUrl("sap/ui2/chips/sample/links/loading.gif");