Fabric: Cleaning up Shadow Tree on surface unregistering

Summary: As it mentioned in the comment, we have to commit an empty tree as part of cleaning up Surface.

Reviewed By: mdvacca

Differential Revision: D9931320

fbshipit-source-id: 04e780bafdb917adeb89f2edef2dc0348b2a4d4a

ReactCommon/fabric/uimanager/Scheduler.cpp

@@ -54,6 +54,8 @@ void Scheduler::unregisterRootTag(Tag rootTag) {
   const auto &iterator = shadowTreeRegistry_.find(rootTag);
   const auto &shadowTree = iterator->second;
   assert(shadowTree);
+  // As part of stopping the Surface, we have to commit an empty tree.
+  shadowTree->complete(std::const_pointer_cast<SharedShadowNodeList>(ShadowNode::emptySharedShadowNodeSharedList()));
   shadowTree->setDelegate(nullptr);
   shadowTreeRegistry_.erase(iterator);
 }