The test was flaky because waiting for scrolling didn't actually wait,
as the page logged a scroll position change to 0/0 directly after
loading.
We work around this by making the generic "And I wait until the scroll
position changed" not wait when it changed to 0/0.
We had some funny segfaults reported during scrolling (i.e. with
QApplication.sendEvent), and some code already had to use postpone=True
so there was no segfault...
So now we're back to postEvent again, and eliminated the main reason for
segfaults with it, which was re-using (and -posting) events which had
already been posted.
At least during tests this seems to run stable, let's hope it helps for
the people having crashes as well.
From the QApplication.postEvent docs:
http://doc.qt.io/qt-5/qcoreapplication.html#postEvent
The event must be allocated on the heap since the post event queue
will take ownership of the event and delete it once it has been
posted. It is not safe to access the event after it has been posted.
We can't reliably guarantee that from Python, so we need to use
sendEvent instead.
