native-fetcher: remove a DCHECK that possibly fires on shutdown.
native-fetcher: remove a DCHECK that possibly fires on shutdown.

wanrui/ngx_pagespeed,digideskio/ngx_pagespeed,digideskio/ngx_pagespeed,wanrui/ngx_pagespeed,0x0mar/ngx_pagespeed,0x0mar/ngx_pagespeed