![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  
B
       o
      if (trackedPath !== null) {
        mightBeOnTrackedPath = true;
      }
       If we have not been profiling, then we can just walk the tree and build up its current state as-is.
      hook.getFiberRoots(rendererID).forEach(root => {
        currentRootID = getOrGenerateFiberID(root.current);
        setRootPseudoKey(currentRootID, root.current);
         H
        if (isProfiling && rootSupportsProfiling(root)) {
           I
           T
          currentCommitProfilingMetadata = {
            changeDescriptions: recordChangeDescriptions ? new Map() : null,
            durations: [],
            commitTime: getCurrentTime() - profilingStartTime,
            maxActualDuration: 0,
            priorityLevel: null,
            updaters: getUpdatersList(root),
            effectDuration: null,
            passiveEffectDuration: null,
          };
        }
        mountFiberRecursively(root.current, null, false, false);
        flushPendingEvents(root);
        currentRootID = -1;
      });
    }
  }