![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  
if (trackedPath === null || !mightBeOnTrackedPath) {
       F
      return false;
    }
    const returnFiber = fiber.return;
    const returnAlternate = returnFiber !== null ? returnFiber.alternate : null;
     By now we know there's some selection to restore, and this is a new Fiber.
     Is this newly mounted Fiber a direct child of the current best match?
     (This will also be true for new roots if we haven't matched anything yet.)
    if (
      trackedPathMatchFiber === returnFiber ||
      (trackedPathMatchFiber === returnAlternate && returnAlternate !== null)
    ) {
       I
      const actualFrame = getPathFrame(fiber);
      const expectedFrame = trackedPath[trackedPathMatchDepth + 1];
      if (expectedFrame === undefined) {
        throw new Error('Expected to see a frame at the next depth.');
      }
      if (
        actualFrame.index === expectedFrame.index &&
        actualFrame.key === expectedFrame.key &&
        actualFrame.displayName === expectedFrame.displayName
      ) {
         W
        trackedPathMatchFiber = fiber;
        trackedPathMatchDepth++;
         A
        if (trackedPathMatchDepth === trackedPath.length - 1) {
           T