![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  
resolvedContext = fiber.type._context || fiber.type;
            
            
            return `${resolvedContext.displayName || 'Context'}.Consumer`;
          case STRICT_MODE_NUMBER:
          case STRICT_MODE_SYMBOL_STRING:
            return null;
          case PROFILER_NUMBER:
          case PROFILER_SYMBOL_STRING:
            return `Profiler(${fiber.memoizedProps.id})`;
          case SCOPE_NUMBER:
          case SCOPE_SYMBOL_STRING:
            return 'Scope';
          default:
            
            
            return null;
        }
    }
  }
  return {
    getDisplayNameForFiber,
    getTypeSymbol,
    ReactPriorityLevels,
    ReactTypeOfWork,
    ReactTypeOfSideEffect,
  };
}
export function attach(