![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
      if (
        alternate == null ||
        treeBaseDuration !== alternate.treeBaseDuration
      ) {
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        const convertedTreeBaseDuration = Math.floor(
          (treeBaseDuration || 0) * 1000,
        );
        pushOperation(TREE_OPERATION_UPDATE_TREE_BASE_DURATION);
        pushOperation(id);
        pushOperation(convertedTreeBaseDuration);
      }
      if (alternate == null || didFiberRender(alternate, fiber)) {
        if (actualDuration != null) {
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          let selfDuration = actualDuration;
          let child = fiber.child;
          while (child !== null) {
            selfDuration -= child.actualDuration || 0;
            child = child.sibling;
          }
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