title: How to get number of URLs already scraped (request_count) from Scrapy?
body: <p>Scrapy show stats like this while running code</p>
  
  <pre><code>2016-11-18 06:41:38 [scrapy] INFO: Dumping Scrapy stats:
  {'downloader/request_bytes': 656,
   'downloader/request_count': 2,
   'downloader/request_method_count/GET': 2,
   'downloader/response_bytes': 2661,
   'downloader/response_count': 2,
   'downloader/response_status_count/200': 2,
   'finish_reason': 'finished',
   'finish_time': datetime.datetime(2016, 11, 18, 14, 41, 38, 759760),
   'item_scraped_count': 2,
   'log_count/DEBUG': 5,
   'log_count/INFO': 7,
   'response_received_count': 2,
   'scheduler/dequeued': 2,
   'scheduler/dequeued/memory': 2,
   'scheduler/enqueued': 2,
   'scheduler/enqueued/memory': 2,
   'start_time': datetime.datetime(2016, 11, 18, 14, 41, 37, 807590)}
  </code></pre>
  
  <p>My goal is to access <code>response_count</code> or <code>request_count</code> in <code>process_response</code> or any method in Spider.</p>
  
  <p>I want to close spider once N number of total URLs are scraped by my Spider.</p>