This patch assumes that only element node can have content node. I.e., we
won't hit the following `MOZ_ASSERT`:
```
Element* element = nullptr;
nsIContent* content = aContent;
while (content) {
if (content->IsElement()) {
element = content->AsElement();
break;
}
content = content->GetParent();
}
MOZ_ASSERT(!content || content == element || content->GetParent() == element);
```
Differential Revision: https://phabricator.services.mozilla.com/D63308
--HG--
extra : moz-landing-system : lando
1110bedb45