WebView flashes when altering page using Javascript

I have the following code that removes some bloat from my reading app.

```
await handlePreferences().then((s) async {
await _fwp.evalJavascript(pageCleaner).then((s) async {
await _fwp.show();
});
});
```

However, the webview flashes when it's shown, and you can see the bloated page for a second before being replaced. Is there a way to fix this?

Start with the reported sequence of handlePreferences, evalJavascript(pageCleaner), and _fwp.show(), then trace how the WebView is displayed during page loading and JavaScript evaluation. Determine why the uncleaned page becomes visible first; done means the WebView no longer flashes the bloated page before cleanup is applied.

Written by the indexing model from the issue text.