![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  
? Array.from(changeDescriptions.entries())
                : null,
            duration: maxActualDuration,
            effectDuration,
            fiberActualDurations,
            fiberSelfDurations,
            passiveEffectDuration,
            priorityLevel,
            timestamp: commitTime,
            updaters,
          });
        });
        dataForRoots.push({
          commitData,
          displayName,
          initialTreeBaseDurations,
          rootID,
        });
      },
    );
    return {
      dataForRoots,
      rendererID,
    };
  }
  function startProfiling(shouldRecordChangeDescriptions: boolean) {
    if (isProfiling) {
      return;
    }
    recordChangeDescriptions = shouldRecordChangeDescriptions;