Each variable contains a reference to the Scala stackframe, not to underlying JDI stackframe. So when this value is updated, it is directly available to the variables.

The stackframes are not recreated to avoid UI flickering. But it likely need a `fireChangeEvent(CONTENT)` to tell the UI to refresh the variable view (if the method called on the VM had side effects).

I think we should keep the FIXME. It needs to have better scaladoc/comments.