onWorkerMessage_(index, event) {
    if (this.disposed) {
      return;
    }
    this.dataLookup_[index] = event.data;
    --this.running_;
    if (this.running_ === 0) {
      this.resolveJob_();
    }
  }
Handle messages from the worker.
@param {number} index The worker index.
@param {MessageEvent} event The message event.