![Screenshot 2019-12-16 10 51 05](https://user-images.githubusercontent.com/793565/70934095-fd91ed80-1ff1-11ea-93b5-746e816585ec.png)
There's seems to be circumstances where unmounted DOM/Fibers are kept alive by React DevTools. They're kept alive in `primaryFibers`:
https://github.com/facebook/react/blob/34527063083195558f98108cde10b5d6ad0d6865/packages/react-devtools-shared/src/backend/renderer.js#L772

It seems like a WeakSet would be appropriate and would remove the leak. Otherwise we'd need to understand why recordUnmount isn't called.

CC @bvaughn  
case SuspenseComponent:
        return 'Suspense';
      case LegacyHiddenComponent:
        return 'LegacyHidden';
      case OffscreenComponent:
        return 'Offscreen';
      case ScopeComponent:
        return 'Scope';
      case SuspenseListComponent:
        return 'SuspenseList';
      case Profiler:
        return 'Profiler';
      default:
        const typeSymbol = getTypeSymbol(type);
        switch (typeSymbol) {
          case CONCURRENT_MODE_NUMBER:
          case CONCURRENT_MODE_SYMBOL_STRING:
          case DEPRECATED_ASYNC_MODE_SYMBOL_STRING:
            return null;
          case PROVIDER_NUMBER:
          case PROVIDER_SYMBOL_STRING:
            
            
            
            resolvedContext = fiber.type._context || fiber.type.context;
            return `${resolvedContext.displayName || 'Context'}.Provider`;
          case CONTEXT_NUMBER:
          case CONTEXT_SYMBOL_STRING: