predictors: Downgrade net priority of prefetch requests.

chrome/browser/predictors/resource_prefetcher.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/predictors/resource_prefetcher.h"
 
 #include <algorithm>
 #include <iterator>
 #include <utility>
 
@@ skipping 122 matching lines @@
         internal::kResourcePrefetchPredictorPrefetchedSizeHistogram,
         prefetched_bytes_ / 1024);
 
     state_ = FINISHED;
     delegate_->ResourcePrefetcherFinished(this, std::move(stats_));
   }
 }
 
 void ResourcePrefetcher::SendRequest(const GURL& url) {
   std::unique_ptr<net::URLRequest> url_request =
-      delegate_->GetURLRequestContext()->CreateRequest(url, net::LOW, this);
+      delegate_->GetURLRequestContext()->CreateRequest(url, net::IDLE, this);
   host_inflight_counts_[url.host()] += 1;
 
   url_request->set_method("GET");
   url_request->set_first_party_for_cookies(main_frame_url_);
   url_request->set_initiator(url::Origin(main_frame_url_));
   url_request->SetReferrer(main_frame_url_.spec());
   url_request->SetLoadFlags(url_request->load_flags() | net::LOAD_PREFETCH);
   StartURLRequest(url_request.get());
   inflight_requests_.insert(
       std::make_pair(url_request.get(), std::move(url_request)));
@@ skipping 95 matching lines @@
   if (bytes_read <= 0) {
     FinishRequest(request);
     return;
   }
 
   if (bytes_read > 0)
     ReadFullResponse(request);
 }
 
 }  // namespace predictors