[Housekeeping] Move file IO to slow pool.

net/url_request/url_request_simple_job.cc

Index: net/url_request/url_request_simple_job.cc
diff --git a/net/url_request/url_request_simple_job.cc b/net/url_request/url_request_simple_job.cc
index 4f8b01ab3a7ca29de1ebf9c097e46ba72980afe9..31f8800d803b66bd72f180135f9f9ceab2db51f4 100644
--- a/net/url_request/url_request_simple_job.cc
+++ b/net/url_request/url_request_simple_job.cc
@@ -36,9 +36,8 @@ URLRequestSimpleJob::URLRequestSimpleJob(URLRequest* request,
                                          NetworkDelegate* network_delegate)
     : URLRangeRequestJob(request, network_delegate),
       next_data_offset_(0),
-      task_runner_(base::WorkerPool::GetTaskRunner(false)),
-      weak_factory_(this) {
-}
+      task_runner_(base::WorkerPool::GetTaskRunner(true)),
+      weak_factory_(this) {}
 
 void URLRequestSimpleJob::Start() {
   // Start reading asynchronously so that all error reporting and data