![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 (!hasElementUpdatedSinceLastInspected) {
        if (path !== null) {
          let secondaryCategory = null;
          if (path[0] === 'hooks') {
            secondaryCategory = 'hooks';
          }
           If this element has not been updated since it was last inspected,
           we can just return the subset of data in the newly-inspected path.
          return {
            id,
            responseID: requestID,
            type: 'hydrated-path',
            path,
            value: cleanForBridge(
              getInObject(
                ((mostRecentlyInspectedElement: any): InspectedElement),
                path,
              ),
              createIsPathAllowed(null, secondaryCategory),
              path,
            ),
          };
        } else {
           I
           I
          return {
            id,
            responseID: requestID,
            type: 'no-change',
          };