Test suite: wait for the Stop button to vanish after stopping page loading.
Since commit:26d902fe we've been using code proposed on https://labs.riseup.net/code/issues/10116#note-14 that does not make any sense to me: after pressing Escape, what matters is that the Stop button vanishes, i.e. the page has stopped loading, and not the Reload button. Unless I'm very confused and did not get the reasoning behind that code. Spotted by segfault!