function doSourceLoad(resolve, reject) {
      _utils_index_js__WEBPACK_IMPORTED_MODULE_1__.srcLoader.validateSrc(src, loadImageCb, loadVideoCb);
      function loadImageCb(src) {
        self.loadImage(src, resolve);
      }
      function loadVideoCb(src) {
        self.loadVideo(src, resolve);
      }
    }
Determine whether `src` is an image or video. Then try to load the asset, then call back.

@param {string|Element} src - URL or element.
@param {function} cb - Callback to pass texture source to.