predictors: Downgrade net priority of prefetch requests.

chrome/browser/predictors/resource_prefetcher.cc

Index: chrome/browser/predictors/resource_prefetcher.cc
diff --git a/chrome/browser/predictors/resource_prefetcher.cc b/chrome/browser/predictors/resource_prefetcher.cc
index a953216bd6d7d45124669b5740e9980b2f24c0cc..376a673b4f0e8815584c0eb1a879f29e3b1c5cb8 100644
--- a/chrome/browser/predictors/resource_prefetcher.cc
+++ b/chrome/browser/predictors/resource_prefetcher.cc
@@ -116,7 +116,8 @@ void ResourcePrefetcher::TryToLaunchPrefetchRequests() {
 
 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::DEFAULT_PRIORITY, this);

[pasko, 2017/02/16 18:14:40]

nit: net::LOWEST is slightly more readable

   host_inflight_counts_[url.host()] += 1;
 
   url_request->set_method("GET");