how to use resource cache with flutter_webview_plugin

I verify `appCacheEnabled: true` ,
and ``.

but still I can't use cache.

**behavior**:
when app is running, load image only once.
but when I close the app, running again. it will download image or other resource, i check cache storage with application information, it not change storage size.
so, I think cache is only used once.

how can I do?