This issue is a possible crash case. Actually `SessionAccessibility.NativeProvider.setAttached` is called in C++ constructor of `SessionAccessibility`. But native handle is set after calling the constructor. So when `NativeProvider.setAttached` is called, C++ side might not set native handle yet. So we should not call `setAttached` in the constructor. Differential Revision: https://phabricator.services.mozilla.com/D246070