Add a test for downloader middlewares using Deferreds.
Add a test for downloader middlewares using Deferreds.

elacuesta/scrapy,starrify/scrapy,pablohoffman/scrapy,eLRuLL/scrapy,scrapy/scrapy,pablohoffman/scrapy,eLRuLL/scrapy,scrapy/scrapy,elacuesta/scrapy,starrify/scrapy,starrify/scrapy,scrapy/scrapy,dangra/scrapy,pawelmhm/scrapy,dangra/scrapy,elacuesta/scrapy,pawelmhm/scrapy,pawelmhm/scrapy,pablohoffman/scrapy,dangra/scrapy,eLRuLL/scrapy