![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  
D
          mightBeOnTrackedPath = false;
        } else {
           C
          mightBeOnTrackedPath = true;
        }
         I
         t
        return false;
      }
    }
     T
     T
    mightBeOnTrackedPath = false;
     H
    return true;
  }
  function updateTrackedPathStateAfterMount(mightSiblingsBeOnTrackedPath) {
     u
     N
    mightBeOnTrackedPath = mightSiblingsBeOnTrackedPath;
  }
   Roots don't have a real persistent identity.
   A root's "pseudo key" is "childDisplayName:indexWithThatName".
   For example, "App:0" or, in case of similar roots, "Story:0", "Story:1", etc.
   We will use this to try to disambiguate roots when restoring selection between reloads.
  const rootPseudoKeys: Map<number, string> = new Map();
  const rootDisplayNameCounter: Map<string, number> = new Map();
  function setRootPseudoKey(id: number, fiber: Fiber) {
    const name = getDisplayNameForRoot(fiber);