Improved, re:  Regarding: https://bugzilla.mozilla.org/show_bug.cgi?id=1092375

Since these are in order, I would think you could do something a little shorter with "indexOf"…
``` js
let phases = ['began', 'offered', 'voted', 'engaged']
let provePhaseReady = function (phase) {
  let index = phases.indexOf(phase);
  let reqs = [];
  if (index != -1)
    reqs = phases.slice(0, phases.indexOf(phase));
  reqs.forEach(…)
```