![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  
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      targetErrorBoundaryID = isErrored ? id : getNearestErrorBoundaryID(fiber);
    } else {
      targetErrorBoundaryID = getNearestErrorBoundaryID(fiber);
    }
    return {
      id,
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      canEditHooks: typeof overrideHookState === 'function',
      canEditFunctionProps: typeof overrideProps === 'function',
       D
      canEditHooksAndDeletePaths:
        typeof overrideHookStateDeletePath === 'function',
      canEditHooksAndRenamePaths:
        typeof overrideHookStateRenamePath === 'function',
      canEditFunctionPropsDeletePaths:
        typeof overridePropsDeletePath === 'function',
      canEditFunctionPropsRenamePaths:
        typeof overridePropsRenamePath === 'function',
      canToggleError: supportsTogglingError && targetErrorBoundaryID != null,
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      isErrored,
      targetErrorBoundaryID,
      canToggleSuspense:
        supportsTogglingSuspense &&
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        (!isTimedOutSuspense ||