![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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    if (result.source !== null) {
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    if (window.chrome || /firefox/i.test(navigator.userAgent)) {
      console.log(
        'Right-click any value to save it as a global variable for further inspection.',
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  function deletePath(
    type: 'context' | 'hooks' | 'props' | 'state',
    id: number,
    hookID: ?number,