Reloading WebEngineView removes channel and underlying `window.qt`

Reloading the page rendered in a WebEngineView results in the web page unable to access `window.qt` in JavaScript for creating a channel. This is a regression from 5.6.

The object exists on the view creation step and so works on first run through. A `reload()` of the page is enough to lose the object. Is this expected, or a genuine bug? If expected, what should the application do to re-establish the channel/`window.qt` on reload?

Attached is a modified version of http://blog.trumpton.org.uk/2015/09/qt-webengineview-communication-with.html in an attempt to provide a minimal environment - but we stumbled into it on our project over at https://github.com/plexinc/plex-media-player - since reloading the page is a valid error handling state.