[Prerender] Restore request priorities when swapped in

content/browser/loader/resource_scheduler.cc

 // Copyright (c) 2012 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 "content/browser/loader/resource_scheduler.h"
 
 #include <stdint.h>
 #include <set>
 #include <string>
 #include <utility>
@@ skipping 1062 matching lines @@
     scheduled_resource_request->set_request_priority_params(
         new_priority_params);
     return;
   }
 
   Client* client = client_it->second;
   client->ReprioritizeRequest(scheduled_resource_request, old_priority_params,
                               new_priority_params);
 }
 
+void ResourceScheduler::ReprioritizeRequest(net::URLRequest* request,

[Charlie Harrison, 2017/04/12 12:37:26]

Just curious: In practice, is this needed? I couldn't find any caller that
actually uses the intra_priority params.

[droger, 2017/04/12 13:20:54]

Yeah, I was wondering the same thing initially: intra_priority is almost always
0, so maybe we could remove it?

But there is actually one case where images are prioritized depending on their
"screen area":
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/La...

Not sure if this is really useful, but it does happen.

[Charlie Harrison, 2017/04/12 13:37:04]

Ah good catch. Yeah until we address that we should make sure this patch doesn't
mess with them.

+                                            net::RequestPriority new_priority) {
+  int current_intra_priority = 0;
+  auto* existing_request = ScheduledResourceRequest::ForRequest(request);
+  if (existing_request) {
+    current_intra_priority =
+        existing_request->get_request_priority_params().intra_priority;
+  }
+  ReprioritizeRequest(request, new_priority, current_intra_priority);
+}
+
 ResourceScheduler::ClientId ResourceScheduler::MakeClientId(
     int child_id, int route_id) {
   return (static_cast<ResourceScheduler::ClientId>(child_id) << 32) | route_id;
 }
 
 }  // namespace content