![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 isTimedOutSuspense =
      fiber.tag === ReactTypeOfWork.SuspenseComponent &&
      fiber.memoizedState !== null;
    let child = fiber.child;
    if (isTimedOutSuspense) {
       I
      const primaryChildFragment = fiber.child;
      const fallbackChildFragment = primaryChildFragment
        ? primaryChildFragment.sibling
        : null;
       S
      child = fallbackChildFragment ? fallbackChildFragment.child : null;
    }
    while (child !== null) {
       R
       W
      if (child.return !== null) {
        unmountFiberChildrenRecursively(child);
        recordUnmount(child, true);
      }
      child = child.sibling;
    }
  }
  function recordProfilingDurations(fiber: Fiber) {
    const id = getFiberIDThrows(fiber);
    const {actualDuration, treeBaseDuration} = fiber;
    idToTreeBaseDurationMap.set(id, treeBaseDuration || 0);
    if (isProfiling) {
      const {alternate} = fiber;
       I