Detect if Webview scroll reach the end

[Djankey]

I'm implementing the EULA WebView with the "Accept" button which must be visible only when the user scrolls to the bottom of the web page.
The current scroll position is already implemented and it's working great:

webviewPlugin
      ..onScrollYChanged.listen((double offsetY) {
}

Is it possible to get the max scroll value?
(getMaxScrollAmount or similar...)