Fabric: Assert on destruction non-empty of ShadowTreeRegistry

Summary:
Destruction of Scheduler (and ShadowTreeRegistry as part of it) which has some running Surfaces is not a good thing and practically a bug on the application layer.
With this assert we throw early to flag the issue.

Changelog: [Internal] - Dev only assert indicating a broken invariant in ShadowTreeRegistry

Reviewed By: sammy-SC

Differential Revision: D17924491

fbshipit-source-id: 6b7433fe47630e993e7d5b969f3113f96124b6c9

Author: shergin

ReactCommon/fabric/mounting/ShadowTreeRegistry.cpp

@@ -8,6 +8,10 @@
 namespace facebook {
 namespace react {
 
+ShadowTreeRegistry::~ShadowTreeRegistry() {
+  assert(registry_.size() == 0 && "Deallocation of non-empty `ShadowTreeRegistry`.");
+}
+
 void ShadowTreeRegistry::add(std::unique_ptr<ShadowTree> &&shadowTree) const {
   std::unique_lock<better::shared_mutex> lock(mutex_);
 

ReactCommon/fabric/mounting/ShadowTreeRegistry.h

@@ -19,6 +19,7 @@ namespace react {
 class ShadowTreeRegistry final {
  public:
   ShadowTreeRegistry() = default;
+  ~ShadowTreeRegistry();
 
   /*
    * Adds a `ShadowTree` instance to the registry.