code: function loadAndUseImage(obj, crossOrigin, callback) {
    if (isTexImageSource(obj)) {
      setTimeout(function() {
        callback(null, obj);
      });
      return obj;
    }
  
    return loadImage(obj, crossOrigin, callback);
  }
docs: if obj is an TexImageSource then just
  uses it otherwise if obj is a string
  then load it first.
  
  @param {string|TexImageSource} obj
  @param {string} crossOrigin
  @param {function(err, img)} [callback] a callback that's passed an error and the image. The error will be non-null
  if there was an error
  @private