run = (callback, context = undefined) => {
  if (!schedule) {
    initializeRunner();
  }
  if (!workQueueScheduled) {
    // Nothing is currently scheduled, schedule it now.
    schedule();
    workQueueScheduled = true;
  }
  callback = asyncStackTag.wrap(callback, 'goog.async.run');

  workQueue.add(callback, context);
}
Fires the provided callback just before the current callstack unwinds, or as
soon as possible after the current JS execution context.
@param {function(this:THIS)} callback
@param {THIS=} context Object to use as the "this value" when calling the
    provided function.
@template THIS