message: Use the queues size rather than a overflow integer
diff: @@ -28,7 +28,7 @@ class QueuePool {
  }
  // Get number of items waiting to be inserted into a queue.
  - get waitingItems() { return this._overflowCount; }
  + get waitingItems() { return this.overflow.size(); }
  // Add an item to the queue. ID and item are passed directly to the Queue.
  // Index is optional and should be between 0 ~ poolSize-1. It determines
  @@ -54,7 +54,6 @@ class QueuePool {
  // onto the queue pool. We want to return a promise which resolves
  // after the item has finished executing on the queue pool, hence
  // the promise chain here.
  - this._overflowCount++;
  return this.overflow.enqueue(id, {
  id: id,
  item: item,
  @@ -78,7 +77,6 @@ class QueuePool {
  return q.onceFree();
  });
  return Promise.any(promises).then((q) => {
  - this._overflowCount--;
  if (q.size() !== 0) {
  throw new Error(`QueuePool overflow: starvation. No free queues.`);
  }
  