![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  
isSimulated ? 'unmount is simulated' : '',
      );
    }
    if (trackedPathMatchFiber !== null) {
       W
       I
       R
      if (
        fiber === trackedPathMatchFiber ||
        fiber === trackedPathMatchFiber.alternate
      ) {
        setTrackedPath(null);
      }
    }
    const unsafeID = getFiberIDUnsafe(fiber);
    if (unsafeID === null) {
       I
       I
       O
      
       T
      
       T
      return;
    }
     F
    const id = ((unsafeID: any): number);
    const isRoot = fiber.tag === HostRoot;
    if (isRoot) {
       R