keepAlive method
Creates an ImageStreamCompleterHandle that will prevent this stream from being disposed at least until the handle is disposed.
Such handles are useful when an image cache needs to keep a completer alive but does not itself have a listener subscribed, or when a widget that displays an image needs to temporarily unsubscribe from the completer but may re-subscribe in the future, for example when the TickerMode changes.
Implementation
ImageStreamCompleterHandle keepAlive() {
_checkDisposed();
return ImageStreamCompleterHandle._(this);
}