![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  
const keyPath = [];
    while (fiber !== null) {
      keyPath.push(getPathFrame(fiber));
      fiber = fiber.return;
    }
    keyPath.reverse();
    return keyPath;
  }
  function getBestMatchForTrackedPath(): PathMatch | null {
    if (trackedPath === null) {
       N
      return null;
    }
    if (trackedPathMatchFiber === null) {
       W
      return null;
    }
     Find the closest Fiber store is aware of.
    let fiber = trackedPathMatchFiber;
    while (fiber !== null && shouldFilterFiber(fiber)) {
      fiber = fiber.return;
    }
    if (fiber === null) {
      return null;
    }
    return {
      id: getFiberIDThrows(fiber),
      isFullMatch: trackedPathMatchDepth === trackedPath.length - 1,
    };
  }