![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 'props':
          if (instance === null) {
            if (typeof overridePropsRenamePath === 'function') {
              overridePropsRenamePath(fiber, oldPath, newPath);
            }
          } else {
            fiber.pendingProps = copyWithRename(
              instance.props,
              oldPath,
              newPath,
            );
            instance.forceUpdate();
          }
          break;
        case 'state':
          renamePathInObject(instance.state, oldPath, newPath);
          instance.forceUpdate();
          break;
      }
    }
  }
  function overrideValueAtPath(
    type: 'context' | 'hooks' | 'props' | 'state',
    id: number,
    hookID: ?number,
    path: Array<string | number>,
    value: any,
  ): void {
    const fiber = findCurrentFiberUsingSlowPathById(id);
    if (fiber !== null) {