code: function completeJob(loader, job, callback) {
      var nextJob;
  
      loader.jobsInProgress--;
  
      if ((!loader.jobLimit || loader.jobsInProgress < loader.jobLimit) && loader.jobQueue.length > 0) {
          nextJob = loader.jobQueue.shift();
          nextJob.start();
          loader.jobsInProgress++;
      }
  
      callback(job.image, job.errorMsg, job.request);
  }
docs: Cleans up ImageJob once completed.
  @method
  @private
  @param loader - ImageLoader used to start job.
  @param job - The ImageJob that has completed.
  @param callback - Called once cleanup is finished.