When a UIA client first queries us, the accessibility engine hasn't yet been initialised.
Previously, this also meant that we hadn't yet called InitConsumers() to figure out which Windows clients were present.
This in turn meant that we would initially believe UIA should be enabled, even if we later realised NVDA/a Vispero product was present and then believed it should be disabled.
To fix this, call InitConsumers() appropriately if it hasn't been called yet.
Even with the above fix, the following scenario might still be possible:
1. UIA is enabled.
2. A client QueryInterfaces to IRawElementProviderSimple.
3. UIA gets disabled.
4. Only then does the client try to call a method on IRawElementProviderSimple.
In this scenario, LazyInstantiator::MaybeResolveRoot won't set mWeakUia, but the IRawElementProviderSimple method will try to use mWeakUia, causing a crash.
To fix this, add a new RESOLVE_ROOT_UIA macro used by IRawElementProviderSimple methods.
In addition to calling RESOLVE_ROOT, this also checks mWeakUia and fails gracefully if that is null.
Differential Revision: https://phabricator.services.mozilla.com/D247504
f2254a1d58