![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  
break;
      }
      const displayName = getDisplayNameForFiber(child);
      if (displayName !== null) {
         P
         W
        if (typeof child.type === 'function') {
           T
           t
          preferredDisplayName = displayName;
        } else if (fallbackDisplayName === null) {
          fallbackDisplayName = displayName;
        }
      }
      if (preferredDisplayName !== null) {
        break;
      }
      child = child.child;
    }
    return preferredDisplayName || fallbackDisplayName || 'Anonymous';
  }
  function getPathFrame(fiber: Fiber): PathFrame {
    const {key} = fiber;
    let displayName = getDisplayNameForFiber(fiber);
    const index = fiber.index;
    switch (fiber.tag) {
      case HostRoot: