You as the user can't tell if the webview is using the HTTPS protocol to request data. You don't have to be a target of the NSA to care about this. If you're at a wifi hotspot with your mobile phone, like at the airport, you can see the clear text requests others on the wifi network are making.

You can see what a form posts to when you submit it in the URL. Browsers will warn you when there is non HTTPS data loaded on an HTTPS page.