handler = function() {
    self.emitEvent(wtf.replay.graphics.Playback.EventType.STEP_STARTED);
    self.subStepId_ = -1;
    for (var it = stepToPlayFrom.getEventIterator(); !it.done(); it.next()) {
      self.realizeEvent_(it);
    }
    ++self.currentStepIndex_;
    self.emitEvent(wtf.replay.graphics.Playback.EventType.STEP_CHANGED);
    self.issueStep_();
  }
Plays all the calls in a step and then subsequent steps.
@private