Initially Flow was complaining on line 70 because this.currentCalls is keyed on QueuedCommandType, not string. After I fixed that, Flow started complaining on line 69 due to invalid-computed-prop (computed props must be string or number), so I added a cast to string.
NOTE: CI will fail on this diff. I considered the possibility of fixing Flow errors BEFORE upgrading Flow, but it wasn't possible... in some cases, the fixes to support the new version of Flow caused errors in the old version. I could have hidden these type errors with $FlowFixMe lines and then later revert those, but that seemed like too much busy work.
Depends on D10043