Qt WebEngine: QWebEngineView stops rendering on workspace switch

Attached is a 3-liner test app that triggers the issue. It opens two QMainWindows with embedded QWebEngineViews, loading identical JavaScript timers into both. Steps to replicate:

1. Run app
2. Move both timer windows to a different workspace, say workspace #2 (one easy way to do this is: right-click on window titlebar and select "Move to Workspace Right")
3. Now switch to workspace #1, wait for 10 seconds, and switch back to workspace #2
4. On Fedora 22, if you repeat step (3), 8 times out of 10, you will find that one of the timers on workspace #2 has stopped updating while the other one ticks away. The one that's still ticking is the one that has focus.

Additional observations:

• On Fedora 22, giving focus to the stuck window brings it back to life again (i.e., rendering resumes as if nothing had happened, timers are back in sync, again indicating JS execution was likely never paused).
• On Fedora 20, rendering stops consistently and permanently in both windows, there is no way to even scroll the page. Additionally on Fedora 20, the same symptoms are also triggered by minimizing the windows, waiting a few seconds, and un-minimizing again (this is similar to QTBUG-50818).
• CPU is still consumed by both QtWebEngineProcesses, indicating that JS execution continues and only rendering is paused. This kinda looks like a Chromium / Blink optimization to me.
• Issue does not occur on Fedora 22 + GNOME Shell

Related: QTBUG-50818