1. override
ImageStreamCompleter load(AssetBundleImageKey key)

Converts a key into an ImageStreamCompleter, and begins fetching the image using loadAsync.

Source 

@override
ImageStreamCompleter load(AssetBundleImageKey key) {
  return new OneFrameImageStreamCompleter(
    loadAsync(key),
    informationCollector: (StringBuffer information) {
      information.writeln('Image provider: $this');
      information.write('Image key: $key');
    }
  );
}