Is there a way to show a progress indicator while waiting for page to load?

I'm loading a page generated by a cloud function so it can take a couple of seconds.
Is there a way to show a waiting or progress indicator..?
In the code for WebviewScaffold I see you return a standard scaffold with a circular progress indicator but it immediately gets hidden by the webview .launch() method.

Would be cool if we cloud have the "hidden" parameter also exposed by WebviewScaffold so that we could see the underlying circular progress indicator. Then maybe an onstate change handler to show() the webview once the page is loaded?

I can give this a crack myself... but wondering if there is an alternative or better way?

Start with WebviewScaffold and the webview .launch() call described in the issue. Determine whether exposing the hidden parameter and a page-loaded state callback can keep the indicator visible until loading completes; done means a supported way to show progress during page loading.

Written by the indexing model from the issue text.