Investigate Accessibility problems

[iefremov]

Follow-up to #13778

We fixes a crash occured in accessibilityAttributedStringForRange, this function is called by MacOS for different elements of the browser UI. For some reason, MacOS calls it for Tabs, and in this unfortunate case the requested string cannot be obtained:

- (id)AXValue {
  ax::mojom::Role role = _node->GetData().role;
  if (role == ax::mojom::Role::kTab)
    return [self AXSelected];

for kTab it returns the result of [self AXSelected], which is a bool, it crashes accessibilityAttributedStringForRange

We have to figure out why this happens at all, because Chrome doesn't look affected