![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 (isProfilingSupported) {
        recordProfilingDurations(nextFiber);
      }
    }
    if (shouldResetChildren) {
       W
       s
      if (shouldIncludeInTree) {
         N
        let nextChildSet = nextFiber.child;
        if (nextDidTimeOut) {
           S
          const nextFiberChild = nextFiber.child;
          nextChildSet = nextFiberChild ? nextFiberChild.sibling : null;
        }
        if (nextChildSet != null) {
          recordResetChildren(nextFiber, nextChildSet);
        }
         W
         S
        return false;
      } else {
         L
        return true;
      }
    } else {
      return false;
    }
  }
  function cleanup() {