Bug 1551825 - Release mAnchorJumpElm and mInvalidationList in DocAccessible::Shutdown. r=Jamie

Differential Revision: https://phabricator.services.mozilla.com/D32197

--HG--
extra : moz-landing-system : lando

accessible/generic/DocAccessible.cpp

@@ -435,6 +435,9 @@ void DocAccessible::Shutdown() {
   mDependentIDsHashes.Clear();
   mNodeToAccessibleMap.Clear();
 
+  mAnchorJumpElm = nullptr;
+  mInvalidationList.Clear();
+
   for (auto iter = mAccessibleCache.Iter(); !iter.Done(); iter.Next()) {
     Accessible* accessible = iter.Data();
     MOZ_ASSERT(accessible);