Comment 9 for bug 1499419

I'm seeing something similar with Mnemosyne, which uses QtWebEngine, which itself appears to use code from Chromium.

```
python3: ../nouveau/pushbuf.c:723: nouveau_pushbuf_data: Assertion `kref' failed.
Received signal 6
#0 0x7f0bdb1fb9ee <unknown>
#1 0x7f0bdb1fbb00 <unknown>
#2 0x7f0bdb1fc137 <unknown>
#3 0x7f0be3602100 <unknown>
#4 0x7f0be3602077 gsignal
#5 0x7f0be35e3535 abort
#6 0x7f0be35e340f <unknown>
#7 0x7f0be35f3142 __assert_fail
#8 0x7f0bc43f146f nouveau_pushbuf_data
#9 0x7f0bc43f13d3 nouveau_pushbuf_data
#10 0x7f0bc43f14ff <unknown>
#11 0x7f0bc43f194f <unknown>
#12 0x7f0bc43f2540 nouveau_pushbuf_kick
#13 0x7f0bc4c246c6 <unknown>
#14 0x7f0bc486c38e <unknown>
#15 0x7f0bc486c400 <unknown>
#16 0x7f0bd8e4713b <unknown>
#17 0x7f0bd8e472a6 <unknown>
#18 0x7f0bdfd1af4b QObject::event()
#19 0x7f0be06eec6b QWidget::event()
```

Running Ubuntu 18.10 with kernel 4.18.0-15-generic (module srcversion is 98986FAF1F2E3BC89E0DF0E).