[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 219 matching lines @@
     DCHECK(!request_->GetUserData(kUserDataKey));
     request_->SetUserData(kUserDataKey, new UnownedPointer(this));
   }
 
   ~ScheduledResourceRequest() override {
     request_->RemoveUserData(kUserDataKey);
     scheduler_->RemoveRequest(this);
   }
 
   static ScheduledResourceRequest* ForRequest(net::URLRequest* request) {
-    return static_cast<UnownedPointer*>(request->GetUserData(kUserDataKey))
-        ->get();
+    UnownedPointer* pointer =
+        static_cast<UnownedPointer*>(request->GetUserData(kUserDataKey));
+    return pointer ? pointer->get() : nullptr;
   }
 
   // Starts the request. If |start_mode| is START_ASYNC, the request will not
   // be started immediately.
   void Start(StartMode start_mode) {
     DCHECK(!ready_);
 
     // If the request was cancelled, do nothing.
     if (!request_->status().is_success())
       return;
@@ skipping 821 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,
+                                            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