Bug 1474814: Invalidate the AccessibleHandler cache on focus events. r=MarcoZ

We don't fire a state change for the focused state, since that would be redundant given that we fire a focus event.
However, that also means the handler cache previously didn't get invalidated when there was a focus change without any other update.
That resulted in stale focused states, which could mean an object was exposed as focused when it wasn't.
Invalidating the cache for focus events ensures the focused state is always up to date.

MozReview-Commit-ID: DZTJMbiTwgt

--HG--
extra : rebase_source : 9977699999218432b07c4af2149cba6e0de466af

accessible/windows/msaa/AccessibleWrap.cpp

@@ -1175,6 +1175,7 @@ IsHandlerInvalidationNeeded(uint32_t aEvent)
     case EVENT_OBJECT_NAMECHANGE:
     case EVENT_OBJECT_DESCRIPTIONCHANGE:
     case EVENT_OBJECT_VALUECHANGE:
+    case EVENT_OBJECT_FOCUS:
     case IA2_EVENT_ACTION_CHANGED:
     case IA2_EVENT_DOCUMENT_LOAD_COMPLETE:
     case IA2_EVENT_DOCUMENT_LOAD_STOPPED: